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#1
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Brook 10C's
OMG!!
To think I had my mitts on one of these 30+ years ago and let it go....*sigh*.....and that 10C had a potted IST Mark http://www.ebay.com/itm/Brook-10C-Am...em3a 6b05b511 |
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#2
Posted to rec.audio.tubes
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Brook 10C's
In article ,
"MarkS" wrote: OMG!! To think I had my mitts on one of these 30+ years ago and let it go....*sigh*.....and that 10C had a potted IST Mark http://www.ebay.com/itm/Brook-10C-Am...t=Vintage_Elec tronics_R2&hash=item3a6b05b511 At that price you would think they could include the 300B output tubes! -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
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#3
Posted to rec.audio.tubes
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Brook 10C's
On Oct 10, 2:35*am, John Byrns wrote:
In article , *"MarkS" wrote: OMG!! To think I had my mitts on one of these 30+ years ago and let it go....*sigh*.....and that 10C had a potted IST Mark http://www.ebay.com/itm/Brook-10C-Am...3639313?pt=Vin.... tronics_R2&hash=item3a6b05b511 At that price you would think they could include the 300B output tubes! -- Regards, John Byrns Surf my web pages at, *http://fmamradios.com/ The last current bid was $17,800, bidding had ended, and and the reserve not met. I'd have given $100 each for such old boatanchor junk, knowing one would have to gut them entirely and re-build them. The IST is not a potted tranny, merely a bell ended thinge. OPT and PT are not potted, and look like Old Hammonds, and a bit rusty. New PSU caps have been placed badly on the chassis leaving two big holes where old style electros were used. Wiring under the chassis is a complete rat's nest, and has probably been repaired/modified umpteen times. There are no 2A3 to be seen anywhere. These are very ordinary old crappy amps. But of course some ppl think they are worth $18,000, and its a just another reminder of how stupid the world is. I guess some ppl think a worn out 1955 Ford or 1955 bicycle might be worth the same money. Patrick Turner. |
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#4
Posted to rec.audio.tubes
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Brook 10C's
"Patrick Turner" wrote in message ... On Oct 10, 2:35 am, John Byrns wrote: In article , "MarkS" wrote: OMG!! To think I had my mitts on one of these 30+ years ago and let it go....*sigh*.....and that 10C had a potted IST Mark http://www.ebay.com/itm/Brook-10C-Am...3639313?pt=Vin... tronics_R2&hash=item3a6b05b511 At that price you would think they could include the 300B output tubes! -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ The last current bid was $17,800, bidding had ended, and and the reserve not met. I'd have given $100 each for such old boatanchor junk, knowing one would have to gut them entirely and re-build them. The IST is not a potted tranny, merely a bell ended thinge. OPT and PT are not potted, and look like Old Hammonds, and a bit rusty. New PSU caps have been placed badly on the chassis leaving two big holes where old style electros were used. Wiring under the chassis is a complete rat's nest, and has probably been repaired/modified umpteen times. There are no 2A3 to be seen anywhere. These are very ordinary old crappy amps. But of course some ppl think they are worth $18,000, and its a just another reminder of how stupid the world is. I guess some ppl think a worn out 1955 Ford or 1955 bicycle might be worth the same money. Patrick Turner. I sure would not be the one buying them for $17K either but I wish I kept the one I had (the one with the potted IST). FWIW, that amp sounded pretty damn good driving a JBL monitor. The source being an Ampex 351...now there's a combination you don't see everyday. Anyway, here is a link to the schematic for those interested in the "sliding bias" circuit: http://ampslab.com/vintage_brook10c.htm Thanks, Mark |
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#5
Posted to rec.audio.tubes
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Brook 10C's
"MarkS" being an Ampex 351...now there's a combination you don't see everyday. Anyway, here is a link to the schematic for those interested in the "sliding bias" circuit: http://ampslab.com/vintage_brook10c.htm ** The diode in the low voltage supply looks like it is drawn back to front. Be a positive supply as shown. Voltages are missing too. ..... Phil |
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#6
Posted to rec.audio.tubes
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Brook 10C's
"flipper" wrote in message ... On Tue, 11 Oct 2011 21:51:01 -0400, "MarkS" wrote: snip I sure would not be the one buying them for $17K either but I wish I kept the one I had (the one with the potted IST). FWIW, that amp sounded pretty damn good driving a JBL monitor. The source being an Ampex 351...now there's a combination you don't see everyday. Anyway, here is a link to the schematic for those interested in the "sliding bias" circuit: http://ampslab.com/vintage_brook10c.htm Thanks, Mark Almost everyone seems to call that scheme "sliding bias," perhaps because of Broskie's description, but unless I misread his article it may be the one time he totally misunderstands a circuit as it's purpose is to keep bias constant and not, as the 'conventional wisdom' seems to claim, 'push it into Class AB'. The design was patented by Lincoln Walsh and works on an observation he made that if you sum the two output tube's cathode currents the minimum seen is twice the idle current. That observation is trivial in the idle and Class A condition, since a sine averages to idle, and two tubes make for twice the idle current. In Class AB the average current increases, which everyone who's built a cathode bias Class AB amp knows of as cathode bypass cap charge up. However, if you look at the cathode current waveforms you'll see that the point where the two tube's cathode current crosses over (from one tube to the other) the current sum is, again, twice idle and is the lowest point of the sum. So the trick is to 'capture' that minimum, which is what the first half of the 6SN7 does. With it's grid grounded a 'low' cathode voltage causes it to conduct, pulling down the cap on it's plate. As cathode voltage rises it cuts off and the cap holds that charge subject to it's long time constant with the resistor network. But before it can rise significantly another 'minimum' occurs pulling it back down. This is an interesting principle of automatically maintaining bias. Obviously it can be used with pentodes. Of course, today the circuit would benefit from using semiconductors and op-amps. The best would be to also balance average DC currents in both tubes. I am trying to think of an elegant solution. Relatively small current sensing resistors (47R or so) in the cathodes and a couple of op-amps will probably do the job. Such old ones like LF356 and even LM301 are capable of working with the common mode close to positive rail. At the same time they permit 30...36V supply voltage. This makes possible to make a circuit powered from only one negative supply of about --30...35V. This range would be sufficient to bias majority of useful pentodes. In short, it 'holds' that twice idle current value, albeit with some ripple. There's also some error due to the short duration time of the minimum limiting how 'close' the cap get's pulled down but the voltage is essentially the same, within reason, as would be there during idle or Class A operation. The second half of the 6SN7 is simply an inverting 'level shifter' amp that translates the cap voltage into one appropriate for output tube grid bias. Rather than a "siding bias" the purpose was to keep bias fixed, as in fixed bias, but has the 'feature' of being automatic. Wash, and Brook, called it "Automatic Bias Control." |
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#7
Posted to rec.audio.tubes
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Brook 10C's
"flipper" wrote in message ... I have, in fact, toyed with the same idea and run simulations using both opamp and discrete transistor configurations but was never quite satisfied with the results. Although, it worked well enough (sim) that I posted one of the configurations in the 'experimental' section. http://flipperhome.dyndns.org/Full%2...xed%20Bias.htm From idle at about -8.53V bias to the MOSFET gate (bias at the tube grid is about -10.2V) the shift at max power out is to about -9.1V bias on the MOSFET. Idle current shift from 'normal' to simulating it with double 6BQ5s on both sides was from 36.1mA to 37.7mA. Not bad at all considering that's only 4.4% for what would otherwise be twice the current from 'double tubes'. As the description says, the 'autobias' was tacked onto the previous 'balance' circuit, here http://flipperhome.dyndns.org/6gk6%2...ed%20fixed.htm Btw, balance with that servo is like within 25uA. If you do try something similar I caution to look out for startup surge because the bias wants to 'naturally' slam against the positive limit before the tubes begin conducting and if you have a very long time constant, which is desirable, the tubes will heavily surge if they warm up faster than the bias circuit responds. That's made doubly worse with dual servos because you probably want one of them a 'lot' slower than the other to keep them from feedbacking into each other. That makes one think of adding a 'startup timer' to keep bias full negative till the tubes are warm and then let it slowly rise to setpoint. I thought of using voltage limiters which would not allow the DC grid bias to go higher than some practical figure, say --12V (depending on tubes and operation point). Thus on power-up the tubes will probably run with some excessive but not dangerous current, but then the servo will bring it down. As I said, though, it gets more complicated in practice than the theory suggests. Very impressive circuits! For a start I can see that your balancing differential integrator is unbalanced in itself. You need another 0.22uF cap from non-inverting input of the op-amp to GND. Then you will not need to filter ripple, and two caps C1 and C11 will go. (Then your can combine your four 220K resistors R40, R28, R29, R39 into two 470K). A pole caused by C1 and C11 will go, which is good for stability of the balancing servo. Another flaw is lack of explicit current source or pull-up at C9. It uses base current of Q9 as pull-up. You would agree that beta can vary greatly which makes time constant of your peak detector a bit rubbery. Better to use some fixed definite pull-up (probably about 3.3M) from C9 to +15V, and use a p-MOSFET (BSS138) instead of Q9. |
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#8
Posted to rec.audio.tubes
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Brook 10C's
On Oct 12, 12:51*pm, "MarkS" wrote:
"Patrick Turner" wrote in message ... On Oct 10, 2:35 am, John Byrns wrote: In article , *"MarkS" wrote: OMG!! To think I had my mitts on one of these 30+ years ago and let it go....*sigh*.....and that 10C had a potted IST Mark http://www.ebay.com/itm/Brook-10C-Am...3639313?pt=Vin... tronics_R2&hash=item3a6b05b511 At that price you would think they could include the 300B output tubes! -- Regards, John Byrns Surf my web pages at, *http://fmamradios.com/ The last current bid was $17,800, bidding had ended, and and the reserve not met. I'd have given $100 each for such old boatanchor junk, knowing one would have to gut them entirely and re-build them. The IST is not a potted tranny, merely a bell ended thinge. OPT and PT are not potted, and look like Old Hammonds, and a bit rusty. New PSU caps have been placed badly on the chassis leaving two big holes where old style electros were used. Wiring under the chassis is a complete rat's nest, and has probably been repaired/modified umpteen times. There are no 2A3 to be seen anywhere. These are very ordinary old crappy amps. But of course some ppl think they are worth $18,000, and its a just another reminder of how stupid the world is. I guess some ppl think a worn out 1955 Ford or 1955 bicycle might be worth the same money. Patrick Turner. I sure would not be the one buying them for $17K either but I wish I kept the one I had (the one with the potted IST). FWIW, that amp sounded pretty damn good driving a JBL monitor. The source being an Ampex 351...now there's a combination you don't see everyday. I have no doubts about the ability of 2A3 in PP and driven by 6J5 to give superlative sound as you claim. Anyway, here is a link to the schematic for those interested in the "sliding bias" circuit: http://ampslab.com/vintage_brook10c.htm Yes, interesting. The total common bias Ik for either 2A3 of 300B ( or 6550 ) if used is sensed by 15r Rk of RH 1/2 6SN7. So as output Ek rises, the two stage 6SN7 DC amp generates a negative going grid signal applied to IST sec and hence to the two grids of 6J5 CF driver buffers which allow Class AB2 operation. Its NOT sliding bias at all, ( IMHO ) , just bias regulation which allows either 2A3 or 300B to be used. Sliding bias is where you have a low level of Ia at idle, and as the signal increases the bias Ia in OP tubes is *increased* to keep the amp in class A, Such a scheme may be made to work off a rectifier diode and cap from the signal output. Some limitation to the increase Ia is needed, and I can't think of aqnyone doing such stuff. It could be done in high PO SE amps which spend most of their lives wearing out their tubes and causing el mucho greehouso gasso because max Pda is at idle, and audiophiles usually listen to PO = 1/30 of the max PO where that is say 30W. The Si diode is definately shown wrong way around; it has to make a negative voltage for the bottom of the 6J5 Rks of 27k, and for biasing 6J5 grids on CF. Sometimes someone puts a diode in wrong, and it helps everyone stay awake at least, or run around looking for a fire extinguisher - tube amps are fun you you should know. But of course the Brook circuit working relies on fairly equal character 2A3 and 6J5. The bias grid signal controlled by common Ek in 15r under 1/2 6SN7. OP tube bias current signal is common, not balanced, and if it was, then each OP tube gets its own little bias signal to keep it happy without sharing the same signal with its mate. Balanced bias servo circuits act to balance the Ia in each 1/2 primary, thus minimising OPT core saturation where Idc is unbalanced. But when bias Ik control correction becomes balanced, then you have differential application of the bias grid voltage and then you have a potentially very unstable amp at LF, especially in the case of the Brook with 4 tube input/ driver stages including an IST. Its all so very easy to try to build an amp, but end up with a phase shift oscillator. The Brook is not my cup of tea, well, not for $17k. Anyone could build a better tube amp for maybe -20dB less bucks if they DIY it. Patrick Turner. Thanks, Mark- Hide quoted text - - Show quoted text - |
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#9
Posted to rec.audio.tubes
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Brook 10C's
On Oct 12, 5:58*pm, flipper wrote:
On Tue, 11 Oct 2011 21:51:01 -0400, "MarkS" wrote: snip I sure would not be the one buying them for $17K either but I wish I kept the one I had (the one with the potted IST). FWIW, that amp sounded pretty damn good driving a JBL monitor. The source being an Ampex 351...now there's a combination you don't see everyday. Anyway, here is a link to the schematic for those interested in the "sliding bias" circuit: http://ampslab.com/vintage_brook10c.htm Thanks, Mark Almost everyone seems to call that scheme "sliding bias," perhaps because of Broskie's description, but unless I misread his article it may be the one time he totally misunderstands a circuit as it's purpose is to keep bias constant and not, as the 'conventional wisdom' seems to claim, 'push it into Class AB'. The design was patented by Lincoln Walsh and works on an observation he made that if you sum the two output tube's cathode currents the minimum seen is twice the idle current. That observation is trivial in the idle and Class A condition, since a sine averages to idle, and two tubes make for twice the idle current. In Class AB the average current increases, which everyone who's built a cathode bias Class AB amp knows of as cathode bypass cap charge up. However, if you look at the cathode current waveforms you'll see that the point where the two tube's cathode current crosses over (from one tube to the other) the current sum is, again, twice idle and is the lowest point of the sum. So the trick is to 'capture' that minimum, which is what the first half of the 6SN7 does. With it's grid grounded a 'low' cathode voltage causes it to conduct, pulling down the cap on it's plate. As cathode voltage rises it cuts off and the cap holds that charge subject to it's long time constant with the resistor network. But before it can rise significantly another 'minimum' occurs pulling it back down. IMHO, the AC cathode signal fed to 15r looks like a normal full wave rectifier signal and the positive average Vdc at 6SN7 Rk of 15r increases with increasing class AB signals. The positive going Ek causes positive going anode signal in 6SN7 and there is a 1uF to 0V which smooths out the ripple. So a calm +Vdc is applied to other 6SN7 grid, and its anode responds with -Vdc sig to increase the grid bias applied to 6J5 CF grids. The whole circuit is DC coupled so it regulates the idle DC condition, and when AB action happens there is some change to bias Ia, but with music signals the amp would be found to rarely move out of class A so in fact the bias is just regged, and it slides nowhere. In short, it 'holds' that twice idle current value, albeit with some ripple. There's also some error due to the short duration time of the minimum limiting how 'close' the cap get's pulled down but the voltage is essentially the same, within reason, as would be there during idle or Class A operation. The second half of the 6SN7 is simply an inverting 'level shifter' amp that translates the cap voltage into one appropriate for output tube grid bias. Rather than a "siding bias" the purpose was to keep bias fixed, as in fixed bias, but has the 'feature' of being automatic. Wash, and Brook, called it "Automatic Bias Control." Other makers like Leak just used a pair of 600 ohms for Rk and bypass caps of 47uF. One might use 470uF bypasses these days. Action is very nice, and the two OP tubes get the balanced regulation of their Ia, and KT66, KT88, KT90 6L6GC, 5881 all might be used as they bias up all the same without a servo circuit, IST, and the extra 6SN7 and negative supply etc. DC gain is low, so no risk of LF instability. While the PO is always class A, then bias remains very little unchanged. As RLa-a is reduced, action becomes AB, and the Leak or Brook will both try to bias their OP tubes to have less Ia, and in so doing, the amps become like a class B amp with much higher THD. In guitar amps with severe rock'nroll overdrive, and despite fixed bias, the OP tubes work in class C for sustained overdrive. But this never happens in hi-fi amps where genteel audiophiles seldom want a cello to sound louder than if someone was playing a real one right in front of them. Patrick T. |
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#10
Posted to rec.audio.tubes
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Brook 10C's
IMHO, the AC cathode signal fed to 15r looks like a normal full wave
rectifier signal and the positive average Vdc at 6SN7 Rk of 15r increases with increasing class AB signals. So far so good. The positive going Ek causes positive going anode signal It can't because of the long time constant of the anode capacitor. I think you are are wrong because the the ac signal at 6SN7 cathode has an increasing AVERAGE DC voltage after class AB action has begun. Its like a choke input PSU where the ac before the choke contains a whole range of harmonics of the fundemental Fo, plus the average Vdc, 0.63 x Peak AC volts. Similarly, in any diode plus cap input PSU or radio AM detector, the dc signal contained with AC signal flows unimpeded while AC IS reduced to low levels. And BTW, there are such things as 'plate detectors' used in AM radios. The Brook has a version where the detection works to produce Vdc change but very little AC change at an anode. The Brook anode cap is open circuit at 0.0Hz. Sure there is a time constant. But you will find that even if the cap was 100uF, not the 1uF shown, that the Ea will rise if a Vac signal is applied to the cathode with an average positive going DC component due to increased Idc in the two OP tubes. The tube has low plate resistance when on (low Ek) and discharges the cap but when Ek goes positive the anode *tries* to go positive but can't with any speed because of the long RC time constant. Indeed the anode Ea won't go high quickly with just one short pulse burst of class AB action. But continual high Vac at top of 15r Rk WILL have a LASTING Vdc component, so Ea WILL rise, and therefore apply a more positive Vg to 2nd 6SN7, which produces a more negative Ea, which makes the applied 2A3 grid bias go more negative. It works much the same way as having bypassed Rk on OP tubes. The DC CURRENT INCREASE in OP tubes causes the Rk to develop a higher than idle Ek, and any AC currents present get bypassed by Ck, and all the better if Ck = 1,000 uF, not the lousy low values used when Brook was building amps like the 10C. Because this is a feedback circuit minimum Ek will settle around the g-k 'threshold' voltage. I.E. the point where the tube conducts and above which it is theoretically 'off'. In reality the threshold is not terribly sharp, which limits its effectiveness, and may be why some people misinterpret the thing as a 'sliding bias'. Same kind of problem as if one used the forward drop of an LED as a voltage reference instead of something better like a 2.5V zener. in 6SN7 and there is a 1uF to 0V which smooths out the ripple. It certainly smoothes 'ripple' all right. Indeed. Using your logic above, though, a simple full wave rectified and cap filtered power supply would be at the 'average' of the input, instead of (near) the peak, but it's not and for the same unequal impedance (and diode steering) reason. I suggest you study plate detectors for AM, and examine basic workings of amplifiers a little more fully. The 'charge' cycle is from the low impedance winding and 'discharge' is through a comparatively high impedance circuit load. It quickly charges up and then slowly discharges so the 'average' is near the AC peak. Same with that 6SN7, except inverted. The anode cap discharge cycle is from the low impedance anode and the slow charge cycle is through the high impedance resistor network. It's going to ripple filter at (near) the minimums. That doesn't explain what's happening. Think more simply and basically. So a calm +Vdc is applied to other 6SN7 grid, and its anode responds with -Vdc sig to increase the grid bias applied to 6J5 CF grids. The whole circuit is DC coupled so it regulates the idle DC condition, and when AB action happens there is some change to bias Ia, but with music signals the amp would be found to rarely move out of class A so in fact the bias is just regged, and it slides nowhere. The design intent isn't because of the music signals, which certainly helps, but the circuit 'filtering' at the Ek minimums. At turn on, the 2A3 have very quick emission start up time due to DH cathodes, but because 6SN7 is slow to turn on, maximum negative bias is being applied to 6J5 grids and to 27k Rk for 6J5, so a low Ia initially exists in 2A3, and low Vdc across 15r. So thus the Ia turn of the 2A3 is delayed and is slightly slower than the 6SN7 turn on time. Its an ingenious soft turn on circuit. Once everything warms up, bias is regged, and the class AB action with high Iac at common Rk of 15r has no effect on biasing, except for the Idc average level which works through the 6SN7 regardless of whatever the Vac may be across the 15r. In short, it 'holds' that twice idle current value, albeit with some ripple. There's also some error due to the short duration time of the minimum limiting how 'close' the cap get's pulled down but the voltage is essentially the same, within reason, as would be there during idle or Class A operation. The second half of the 6SN7 is simply an inverting 'level shifter' amp that translates the cap voltage into one appropriate for output tube grid bias. Rather than a "siding bias" the purpose was to keep bias fixed, as in fixed bias, but has the 'feature' of being automatic. Wash, and Brook, called it "Automatic Bias Control." Other makers like Leak just used a pair of 600 ohms for Rk and bypass caps of 47uF. One might use 470uF bypasses these days. Action is very nice, and the two OP tubes get the balanced regulation of their Ia, and KT66, KT88, KT90 6L6GC, 5881 all might be used as they bias up all the same without a servo circuit, IST, and the extra 6SN7 and negative supply etc. DC gain is low, so no risk of LF instability. Which should be a great big clue they didn't stick a tube in there just to do the same thing as bypassed Rk's. Makers of Leak et all employed bean counters, and bean counters reminded CEOs of profit losses if too much engineer inspired design went in under any chassis. After Brook, some designers were able to give good enough reasons to DUMP the Brook and other ideas favoured by the old *******s of 1950 who liked to stay rooted in the pre WW2 past. Williamson came along to show you just didn't need a Brook bias circuit, or a damned IST, especially if you wished to make a fully and unconditionally stable amp with a useful amount of NFB. Willy made things a lot more difficult for OPT makers, and so he got laughed off the stage with rotten eggs thrown by bean counters and CEOs. **** 'em all, I'll do it my way Flipper. The Brook bias reg circuit could be implemented using a pair of signal transistors, with emitter re to keep gain low as the 6SN7; should work fine, but not really needed. While the PO is always class A, then bias remains very little unchanged. As RLa-a is reduced, action becomes AB, and the Leak or Brook will both try to bias their OP tubes to have less Ia, No, the Brook won't. That is *the purpose* of the 6SN7, to keep a 'fixed bias'. Here again you are wrong. The Vdc signal in 15r Rk RISES when class A action moves to class AB. So this causes a more negative bias voltage to be applied to 2A3. The bias is NOT fixed at all. In a fixed bias amp, Eg remains fixed after a human sets the grid bias pots. Ia is allowed to rise above the idle value and it has no effect on Eg applied bias. This gives the least THD in class AB amps, although if one were to make Eg more positive as Ia anmd Ik rose, then Pda in OP tubes increases so the class A portion of power increases, therefore reducing THD. Its sliding bias. Some SS amps used this, even big fat Marantz amps. All sorts of claims were made about the betterment of sound with increased idle current when signals went higher, but usually you'll find that when you listen to music through an SS amp, and you manually adjust the bias pot to change between class C with devices biased right off for part of the wave cycle, or or adjust the pot for high class A bias current which one would not want to keep doing for long, you hear NO music quality change. This is because the amp probably has 60dB of applied NFB, and the crossover distortion and resultant IMD is virtually all reduced below 0.01% no matter what the bias setting is, and looking at the wave forms confirms this view. I've done this while repairing amps. Tube amps don't have the luxury of having more than 20dB NFB at most, so they need to be linear so class A triodes are used, but where high PO is to be sustained, its usually not a hi-fi situation any more, but a PA sit, so if the amp is biased towards class B and THD moves from 0.2% at 10W to 1% at 25W, nobody worries, its still below 1%. They could, of course, have simply done a plain old pot fixed bias but that wouldn't be self biasing. Pots in the hands of owners are dangerous. People don't bother or forget to adjust bias. and in so doing, the amps become like a class B amp with much higher THD. In their white paper Brook claims the amp will do 30 continuous Class AB2 watts with less than 2.5% distortion. Care to make a guess what distortion would be with the Leak under the same conditions? Well, the Brook would indeed make at least 2.5% at 30W. Leaks with pair of KT66 in triode might give 12W at 0.1% THD, and in AB1 with a lower RLa-a, maybe 2.5%, And more if working in UL mode. One might set up KT66 to work in class AB2 which would allow the triode power to be nearly as high as the UL mode. Sure, expect lots of THD. But while hi-fi music from a pair of 2A3 has an average level far below the maximum AB2 power at 30W+, the peaks in music, drum-beats etc, could rise to the 30W+ level with little THD/IMD increase. The majority of PP tube amps made now act in class A for 95% of most listener requirements, but they move to class AB for transients and during such time the cathode biasing hardly changes. Measure an amp sometime, and you'll soon get to know what really happens. http://www.tubecad.com/2007/12/15/Hi...20Amplifier%20... In guitar amps with severe rock'nroll overdrive, and despite fixed bias, the OP tubes work in class C for sustained overdrive. But this never happens in hi-fi amps Which is why bringing up guitar amp overdrive was utterly irrelevant. We should know how ALL amps, even the Brook 10C would respond to being heavily overdriven. What happens if an audiophile does not notice one speaker lead is shorted? The NFB vastly increases the signal drive to OP tubes, and Ia rises dramatically, so the Brook responds by changing its applied grid bias to much more negative, maybe saving the tubes until the dopey audiophile wakes up about what's wrong. Of course you'd like to prevent me saying stuff, but I just won't **** off and STFU. Patrick Turner. |
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#11
Posted to rec.audio.tubes
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Brook 10C's
On Oct 14, 7:22*pm, flipper wrote:
On Thu, 13 Oct 2011 19:46:41 -0700 (PDT), Patrick Turner wrote: snip of typical Turner arrogant babble http://www.tubecad.com/2007/12/15/Hi...20Amplifier%20.... Read the damn paper, Patrick. That's why I gave you a link to it. I've had a read, and there's nothing which I need to change about what I've said in recent posts about how the Brook amp works. "For best operation, it is desirable that the instantaneous minimum of the sum of the plate currents be held substantially constant at the zero signal value. This abc *circuit is therefore designed to utilize this instantaneous minimum of plate current as the control factor in setting the grid bias, and is substantially unaffected by changes in the average current due to increases in the plate current which occur during the signal cycle. . As the charge on condenser C27 has too short an interval to build up its voltage appreciably, its average voltage remains substantially at the value for zero signal and does not change appreciably when the signal increases from zero to a very large value." All very well as stated in 1947. I did make one mistake in seeing the anode to ground cap for 6SN7 was 1uF, but in fact it was 0.1uF, so that the ripple reduction or Vac shunting at 6SN7 has a time constant 1/10 of what I thought was there, the 1.0 uF, because a decimal point went missing in poor scans of old schematics. I thought 1.0uF was a bit too large a value to do the job, a smaller one would do, because a 1.0uF paper cap rated for 400Vdc would have been a monster, and sent the bean counters into a rabid frenzy over its cost. But C could be 10.0uF, and the circuit would still respond exactly as I said to average dc levels at 2A3 cathodes rising with class AB1 or AB2 action, providing the sine wave signal at the clipping level was maintained. The 1947 article says only 11 dB global NFB is used, and that they tried to ensure least dependance on NFB. The Brook designer shows he had little or no understanding of critical damping and the only attempt at fiddling with open loop response to make the circuit work OK with GNFB and presumably a pure resistance load is the use of 4k7 + 0.001uF LPF before the CF drivers to OP tubes. This probably makes the HF performance worse, and more likely to be unstable at HF. There is no C across the NFB Rfb, 1,000 ohms. I have no details of how the OPT was designed, and unless I knew exactly about the quality of such an important item, I can't agree the old Brook Boatanchor is more better than an old boatanchor, which can be ought for a lot less than $17,000. The performance of the IST is another thing I'd like to know. IMH0, Mr Wiliamson knew rather more than Mr Brook. Mr W knew what to keep OUT of his amps, and he knew more better about what to put IN, and why. Bean counters didn't agree of course with just about anything anyone did, leaving CEOs to vote for profits rather than for excellence in amplifiers. Such wicked shenanigans has led to so only very few mass made amps which are good enough to withstand the glare of public scrutiny. Nowdays, nothing is to be gained by copying a Brook amp; the USAF is NOT about to begin a production run of old Hellcats, although the coming generation of drone attack aircraft are making last year's models look like real dumb turkeys. If you disagree, then say just how and why. Patrick Turner. |
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#12
Posted to rec.audio.tubes
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Brook 10C's
"flipper" wrote in message ... On Fri, 14 Oct 2011 22:30:24 -0700 (PDT), Patrick Turner wrote: On Oct 14, 7:22 pm, flipper wrote: On Thu, 13 Oct 2011 19:46:41 -0700 (PDT), Patrick Turner wrote: snip of typical Turner arrogant babble http://www.tubecad.com/2007/12/15/Hi...20Amplifier%20... Read the damn paper, Patrick. That's why I gave you a link to it. I've had a read, and there's nothing which I need to change about what I've said in recent posts about how the Brook amp works. Then at least we've established you either can't read or think "instantaneous minimum" is an average. And blind as a bat too since he also provides a pretty set of o-scope like pictures in fig 2. showing individual tube currents, the sum currents, where the minimums occur, that they're the same as idle, and the detected bias level being the same, plus ripple, in Class AB as Class A or idle. Partick is only partly right. Because of the not very sharp cutoff of 6SL7, the "trough-detector" 6SN7 it will not be ideally tracking the minima, but will be to some extent "confused" by the average current. Surely if you idle that amp for a while, measure negative bias on 2A3s, then apply a continuous sine-wave for a few seconds and measure the bias again, it will go down (provided the B+ is stable) -- the servo will try to reduce idle current of 2A3s. This is not the intention of the designer though. The intention was to make an ideal trough detector. Today it can be acieved with semiconductors easily. |
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#13
Posted to rec.audio.tubes
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Brook 10C's
Read the damn paper, Patrick. That's why I gave you a link to it.
I've had a read, and there's nothing which I need to change about what I've said in recent posts about how the Brook amp works. Then at least we've established you either can't read or think "instantaneous minimum" is an average. And blind as a bat too since he also provides a pretty set of o-scope like pictures in fig 2. showing individual tube currents, the sum currents, where the minimums occur, that they're the same as idle, and the detected bias level being the same, plus ripple, in Class AB as Class A or idle. I don't get what you mean in this para. The Brook article more or less confirms what I've seen on my scope. But while ever the OP tubes remain in class A, the average Vdc at top of a common Rk will remain about constant. But once you move to class AB where the positive going peak load currents can be 3 times the idle current, then the average Vdc at common Rk rises and a dc meter should confirm this. Put an 8 ohm load onto a Quad-II amp set for 16 ohms and the RLa-a becomes 2k0 approx, and most PO is then AB1, and Ek rises across the bypassed 180 ohm Rk. without the bypass cap, there is still a rise, and if the rise in Ek is amplified by a Vdc amp to increase the negative grid bias, the amp might begin to work in class C ! But at idle and and while in class A, the Brook 10C effectively regulates its Idc total anode current so that one may uses 2A3, 300B, and probably one might use KT88, KT90, 6550, EL34, 6L6, KT66, etc, etc, and as long as the Pda at idle is kept below say 15 watts at idle for each OP tube then all is about well enough - for class A operation. Methinks that high power class Class AB1 or AB2 isn't as good as having plain old fixed bias. The only way to fix the auto cathode bias and keep it fixed during class AB is to shunt excessive load currents as they occur to prevent Vdc rise at cathodes. See my circuits for Dynamic Bias Stabilisation at http://www.turneraudio.com.au/300w-5...tabilizer.html This wasn't really possible in 1947, but had it been, some bright ******* would have invented it and tried to sell amps because they had it and others didn't. To stop tubes melting down during faults, I use active fault detection circuits that were difficult to implement in 1947 because such circuits needed a couple of tubes and a relay sensitve to low currents, ie, a delicate high resistance relay coil. But fault detection circuits are dead easy with a few bjts with SCR and mini R&C bits and a 12V supply. And you can have LEDs to tellya what's wrong, and if the Idc balance is set wrong. The Brook is a nice attempt to sell an amp with yet another you-beaut idea of "automatic bias" whatever. Just about all amps produced have a LOUD subliminal message leading to sales. Bose has a "Lifestyle System". But tiny crummy 2" drivers in matchbox speakers are on ceiling with bass speaker in corner, and kitchen remote. Shiealas fall for such crap, but not me. B&O make a range of truly horrid products. I've had to work on their POSs. Quad amps could have been better. I have bullet holes still healing up after the last time I said that here. But ESL57 were exceptionally good, and I'd hazard a guess the Brook 10C with 300B would be good to drive ESL57 - if you can ever find a pair that work properly after 40 years and which won't cook an amp as I have seen them do when arcing occurs in old panels. My 3.1428 cent's worth, Patrick Turner. "For best operation, it is desirable that the instantaneous minimum of the sum of the plate currents be held substantially constant at the zero signal value. This abc circuit is therefore designed to utilize this instantaneous minimum of plate current as the control factor in setting the grid bias, and is substantially unaffected by changes in the average current due to increases in the plate current which occur during the signal cycle. . As the charge on condenser C27 has too short an interval to build up its voltage appreciably, its average voltage remains substantially at the value for zero signal and does not change appreciably when the signal increases from zero to a very large value." snip of arm waving- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - |
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#14
Posted to rec.audio.tubes
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Brook 10C's
On Oct 15, 7:22*pm, flipper wrote:
On Sat, 15 Oct 2011 17:33:17 +1100, "Alex Pogossov" wrote: "flipper" wrote in message .. . On Fri, 14 Oct 2011 22:30:24 -0700 (PDT), Patrick Turner wrote: On Oct 14, 7:22 pm, flipper wrote: On Thu, 13 Oct 2011 19:46:41 -0700 (PDT), Patrick Turner wrote: snip of typical Turner arrogant babble http://www.tubecad.com/2007/12/15/Hi...20Amplifier%20... Read the damn paper, Patrick. That's why I gave you a link to it. I've had a read, and there's nothing which I need to change about what I've said in recent posts about how the Brook amp works. Then at least we've established you either can't read or think "instantaneous minimum" is an average. And blind as a bat too since he also provides a pretty set of o-scope like pictures in fig 2. showing individual tube currents, the sum currents, where the minimums occur, that they're the same as idle, and the detected bias level being the same, plus ripple, in Class AB as Class A or idle. Partick is only partly right. Because of the not very sharp cutoff of 6SL7, the "trough-detector" 6SN7 it will not be ideally tracking the minima, but will be to some extent "confused" by the average current. I said the same in my description and even speculated that may be why some are fooled into thinking it's a 'sliding bias'. I even gave a solid state analogous example of using a forward biased LED to 'regulate' rather than something better like a zener. Btw, he's using a 6SN7 (7N7). Surely if you idle that amp for a while, measure negative bias on 2A3s, then apply a continuous sine-wave for a few seconds and measure the bias again, it will go down (provided the B+ is stable) -- the servo will try to reduce idle current of 2A3s. This is not the intention of the designer though. The intention was to make an ideal trough detector. Today it can be acieved with semiconductors easily. I also said 'intended design' because I don't know 'how well' their implementation worked. Just for chuckles I stuck a 6SN7 in that solid state circuit as the detector, cathode where the emitter was and grid grounded. I question whether a 'real life' tube would work at 7V and a couple of uA but not only does the simulator let it run but bias was rock solid from 1W to 20W output. A kluge like that doesn't really mean much but it was still surprising.- Hide quoted text - - Show quoted text - Try a real amp with a real tubes, with real meters and a real Mr O'Scope, that Irish truthist. Patrick Turner. |
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#15
Posted to rec.audio.tubes
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Brook 10C's
On Oct 16, 10:07*pm, flipper wrote:
On Sun, 16 Oct 2011 02:56:11 -0700 (PDT), Patrick Turner wrote: Read the damn paper, Patrick. That's why I gave you a link to it. I've had a read, and there's nothing which I need to change about what I've said in recent posts about how the Brook amp works. Then at least we've established you either can't read or think "instantaneous minimum" is an average. And blind as a bat too since he also provides a pretty set of o-scope like pictures in fig 2. showing individual tube currents, the sum currents, where the minimums occur, that they're the same as idle, and the detected bias level being the same, plus ripple, in Class AB as Class A or idle. I don't get what you mean in this para. I mean you can't grasp what's written nor see it put into pretty pictures and you prove it by again claiming 'it says' what you say. It does not and your description is simply flat ass wrong. What the hell do you think they mean by "instantaneous minimum?" The Brook article more or less confirms what I've seen on my scope. That's where the blind as a bat comes in. Figure 2 clearly shows the automatic bias control capturing the voltage minimums and that bias does NOT 'rise' during Class AB operation. snip of flat ass wrong The only way to fix the auto cathode bias and keep it fixed during class AB is to shunt excessive load currents as they occur to prevent Vdc rise at cathodes. Wrong. The Lincoln Walsh "Automatic Bias Control" used by Brook keeps bias fixed at essentially the same level from idle to Class A to Class AB. Here's his patent. Although, if you can't get it from the article I don't know how you're going to get it from the patent. Fig 2 comes straight from it. http://www.freepatentsonline.com/2361889.pdf He explicitly states in the patent: "the plate current rises substantially but the grid bias voltage remains substantially at it's no load value." From the patent I've read, I quote, "...as the bias on the grids of the push-pull amplifier tubes becomes more negative by the the control line, the plate current of these tubes is reduced to a value at which the system finds equilibrium.." So as Vdc average V across 15r increases, the 2A3 grid bias is adjusted to keep their total Ia constant. I have no argument with Mr Walsh to this point, and I agree substantially with all his displayed wave forms. A Vdc voltmeter held across the 15r would show a considerable rise in Vdc when high power class AB action occurs. I'm not sure the the claims about time constants somehow stopping the grid bias change, but the sawtooth wave in the bottom Oscope trace is labelled "rate of rise determined by C27 and R28", and most ripple is filtered away, lest Vac be fed to OP tube grids as well as amplified Vdc bias voltage. The rate of rise I assume is the sawtooth rise, and not the slow change to Vdc bias. But it seems to me that the negative OP tube grid bias DOES INCREASE to keep the total plate current constant regardless of the OP tube loading in class AB when under normal fixed bias operation, total Iadc to the OP tubes can more than double during class AB operation. The conditions for the increase in negative grid bias depend on how long the high power class AB effort is sustained. None of Walsh's wave forms show the variation in applied OP tube bias over a long period of say thousands of times the time for one wave at the test signal frequency. If the test signal is at 400Hz, a common F used for testing amps in 1947, then one might like to know what happens to grid bias voltage over a sustained 30W power level from AB 2A3 over say a 10 second time, and my guess is the bias applied to 2A3 would indeed go very negative, but the trace shown in the patent used to display the sawtooth shows only a tiny number of test signal waves, so you can't see the slow Vdc change. So I see that this Walsh auto biasing method has the same defect of all automatic servo biasing or cathode RC network biasing of class AB tubes if the amp works in class AB, or B, and high levels are sustained. But while the amp works in class A for most of the time, servo bias or cathode biasing is OK. The Walsh auto bias would work better than RC cathode biasing to maintain constant Ia in OP tubes at the idle conditioni, but for lowest THD in class AB, one needs to allow unimpeded rise in total tube Ia and NO CHANGE to all electrode voltages from the condition at idle, which means no fiddling with grid bias, and also means regulating the anode supply, and in 1947, the latter meant using a good choke input plate supply. Why don't ya see the Walsh idea used in many amps? Its not as good as Walsh makes out. I rest my case. If one uses my Dynamic Bias Stabilisation method, no Walsh type of grid voltage fiddle is attempted. Grid bias is kept constant. Cathode biasing is used, and Ek kept constant; Ek hardly rises much regardless of class AB hard work; Ia is allowed to increase as it must to maintain lowest class AB THD, so it is kept low as true fixed bias. If I see something worth copying from Mr Walsh, I might be tempted, but I don't. Patrick Turner. |
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#16
Posted to rec.audio.tubes
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Brook 10C's
On Oct 16, 10:10*pm, flipper wrote:
On Sun, 16 Oct 2011 02:59:29 -0700 (PDT), Patrick Turner wrote: On Oct 15, 7:22*pm, flipper wrote: On Sat, 15 Oct 2011 17:33:17 +1100, "Alex Pogossov" wrote: "flipper" wrote in message .. . On Fri, 14 Oct 2011 22:30:24 -0700 (PDT), Patrick Turner wrote: On Oct 14, 7:22 pm, flipper wrote: On Thu, 13 Oct 2011 19:46:41 -0700 (PDT), Patrick Turner wrote: snip of typical Turner arrogant babble http://www.tubecad.com/2007/12/15/Hi...20Amplifier%20... Read the damn paper, Patrick. That's why I gave you a link to it. I've had a read, and there's nothing which I need to change about what I've said in recent posts about how the Brook amp works. Then at least we've established you either can't read or think "instantaneous minimum" is an average. And blind as a bat too since he also provides a pretty set of o-scope like pictures in fig 2. showing individual tube currents, the sum currents, where the minimums occur, that they're the same as idle, and the detected bias level being the same, plus ripple, in Class AB as Class A or idle. Partick is only partly right. Because of the not very sharp cutoff of 6SL7, the "trough-detector" 6SN7 it will not be ideally tracking the minima, but will be to some extent "confused" by the average current. I said the same in my description and even speculated that may be why some are fooled into thinking it's a 'sliding bias'. I even gave a solid state analogous example of using a forward biased LED to 'regulate' rather than something better like a zener. Btw, he's using a 6SN7 (7N7). Surely if you idle that amp for a while, measure negative bias on 2A3s, then apply a continuous sine-wave for a few seconds and measure the bias again, it will go down (provided the B+ is stable) -- the servo will try to reduce idle current of 2A3s. This is not the intention of the designer though. The intention was to make an ideal trough detector. Today it can be acieved with semiconductors easily. I also said 'intended design' because I don't know 'how well' their implementation worked. Just for chuckles I stuck a 6SN7 in that solid state circuit as the detector, cathode where the emitter was and grid grounded. I question whether a 'real life' tube would work at 7V and a couple of uA but not only does the simulator let it run but bias was rock solid from 1W to 20W output. A kluge like that doesn't really mean much but it was still surprising.- Hide quoted text - - Show quoted text - Try a real amp with a real tubes, with real meters and a real Mr O'Scope, that Irish truthist. Puffery. Why don't you try building the circuit since reading how it works isn't working for you. I've spent many years building tube amps and repairing them. Patrick Turner. |
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#17
Posted to rec.audio.tubes
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Brook 10C's
On Oct 17, 11:59*am, flipper wrote:
On Sun, 16 Oct 2011 16:51:57 -0700 (PDT), Patrick Turner wrote: On Oct 16, 10:10*pm, flipper wrote: On Sun, 16 Oct 2011 02:59:29 -0700 (PDT), Patrick Turner wrote: On Oct 15, 7:22*pm, flipper wrote: On Sat, 15 Oct 2011 17:33:17 +1100, "Alex Pogossov" wrote: "flipper" wrote in message .. . On Fri, 14 Oct 2011 22:30:24 -0700 (PDT), Patrick Turner wrote: On Oct 14, 7:22 pm, flipper wrote: On Thu, 13 Oct 2011 19:46:41 -0700 (PDT), Patrick Turner wrote: snip of typical Turner arrogant babble http://www.tubecad.com/2007/12/15/Hi...20Amplifier%20... Read the damn paper, Patrick. That's why I gave you a link to it. I've had a read, and there's nothing which I need to change about what I've said in recent posts about how the Brook amp works. Then at least we've established you either can't read or think "instantaneous minimum" is an average. And blind as a bat too since he also provides a pretty set of o-scope like pictures in fig 2. showing individual tube currents, the sum currents, where the minimums occur, that they're the same as idle, and the detected bias level being the same, plus ripple, in Class AB as Class A or idle. Partick is only partly right. Because of the not very sharp cutoff of 6SL7, the "trough-detector" 6SN7 it will not be ideally tracking the minima, but will be to some extent "confused" by the average current. I said the same in my description and even speculated that may be why some are fooled into thinking it's a 'sliding bias'. I even gave a solid state analogous example of using a forward biased LED to 'regulate' rather than something better like a zener. Btw, he's using a 6SN7 (7N7). Surely if you idle that amp for a while, measure negative bias on 2A3s, then apply a continuous sine-wave for a few seconds and measure the bias again, it will go down (provided the B+ is stable) -- the servo will try to reduce idle current of 2A3s. This is not the intention of the designer though. The intention was to make an ideal trough detector. Today it can be acieved with semiconductors easily. I also said 'intended design' because I don't know 'how well' their implementation worked. Just for chuckles I stuck a 6SN7 in that solid state circuit as the detector, cathode where the emitter was and grid grounded. I question whether a 'real life' tube would work at 7V and a couple of uA but not only does the simulator let it run but bias was rock solid from 1W to 20W output. A kluge like that doesn't really mean much but it was still surprising.- Hide quoted text - - Show quoted text - Try a real amp with a real tubes, with real meters and a real Mr O'Scope, that Irish truthist. Puffery. Why don't you try building the circuit since reading how it works isn't working for you. I've spent many years building tube amps and repairing them. Irrelevant. You never built the Walsh ABC circuit, clearly can't grasp his own description of it, and never put your "real meters and a real Mr O'Scope" to it.- Hide quoted text - - Show quoted text - Sure I ain't built a Brook 10C. I doubt I'd learn anything I didn't know already because I've built so much other stuff. Have you built a Brook 10C? where are your detailed test results? Building the amp in a simulator does not count. Patrick Turner. |
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#18
Posted to rec.audio.tubes
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Brook 10C's
From the patent I've read, I quote, "...as the bias on the grids of
the push-pull amplifier tubes becomes more negative by the the control line, the plate current of these tubes is reduced to a value at which the system finds equilibrium.." Instead of trying to find snippets to supposedly 'prove' what you already wrongly think try reading to understand it. That entire section begins with "when the static or no signal plate currents of the output tubes..." Yes, it automatically adjusts bias. That's why the title of the patent is "Automatic Bias Control." And what causes the negative bias voltage to output tubes to change to a wanted value? Its the Vdc across the 15 ohms. So as Vdc average V across 15r increases, the 2A3 grid bias is adjusted to keep their total Ia constant. I have no argument with Mr Walsh to this point, You don't even know what the conditions are. No, you don't realise I know all too well what the waveforms tell me. and I agree substantially with all his displayed wave forms. A Vdc voltmeter held across the 15r would show a considerable rise in Vdc when high power class AB action occurs. There is no "Vdc" in Class AB. It's a friggin 'rectified AC waveform', as you once described it. Unfortunately, you cannot recognise where there is a Vdc present as you are blinded by the Vac shown at the top of the 15 ohms. The voltage across the 15 ohms is **always** above 0V. It **cannot go negative**, OK, and the voltage across the 15 ohms pilot sensing resistance is caused by both the AC current constituent and the DC current constituent. When the amp works in class AB with a low load to allow 30W, the positive going Vac peaks at 15 ohms are several times the Vdc found at idle with no signal. If you looked at a full wave power rectifier with CT winding feeding an R load with no C you'd find that there are a procession of half sine wave cycles rising above 0V at the load R, and the average Vdc level = 0.63 x peak Vac, and that the main Vac is twice the fundemental mains F, and that other harmonics are present. What happens in a class AB or class B amp is very similar to a rectifier circuit, and in the Brook the Vdc present at the cathode moves well above the total idle Idc of both tubes x Rk when the amp works in heavy class AB. The 6SN7 with Rk = 15 ohms is turned on fully at idle because very little grid bias is present, and Eg1 = close to 0V. Any rise in Ek due to class AB action in the OP tubes begins to turn off the 6SN7, thus causing a rise in Ea, and this happens with gusto as the 6SN7 is very much alive, and initially well away from cut off. There would be huge Vac changes at the 6SN7 if there was no 0.1uF, but such Vac changes are miniscule with 0.1uF, just a saw tooth wave, but the cap has huge impedance at DC, and the 6SN7 anode Vdc change happens just like in a rectifier. Doesn't matter what a "VDC voltmeter" would say because the circuit doesn't behave as a "VDC voltmeter." It's a voltage minimum '-peak and hold' detector. You just DON'T GET IT. Fourier would be laughing his head off at you. There IS A VDC PRESENT at the cathodes of the 2A3 and its a higher voltage than at idle during class AB action. I'm not sure the the claims about time constants somehow stopping the grid bias change, You're "not sure" because you refuse to follow the operational description. The cap and R time constant does not stop the 2 x 1/2 6SN7 acting as a Vdc direct coupled amplifier. Its the only damn thing its allowed to do !!!!! but the sawtooth wave in the bottom Oscope trace is labelled "rate of rise determined by C27 and R28", Right. The plate voltage is RAPIDLY pulled down by the Ek minimum and then slowly rises, which is why it's a sawtooth. The 'rise' is how much it will deviate from the idle current voltage before being rapidly pulled back down to it again. Forget the Ek minimum for now. Just think first of the idle condition when 1.2Vdc exists aross the 15r. Its a result of 2 x 40mA bias currents flowing in 15r. Now consider the pure class A action of the amp where the Idc flow to 2A3 anodes remains constant. At idle the total tube Pda = say 350V x 80mA = 28W total, and with pure class A PO = say 7W, Pda drops to 21W, with the other 7W liberated as heat in the load. Idc at cathodes remains 2 x 40mA = 80mA and Vdc at cathodes also remains constant. Vac at cathodes is mainly 2H distortion content. But each tube moves close to cut off, but doesn't cut off. The distortion voltage shows that the max ON current swing of each tube exceeds the minimum OFF current of each tube, and because the currents of both tubes with opposite phase currents are present, you just get mainly 2H at k. But it all changes when the load goes to a lower value , and one tries to force the tubes into class AB for 30Watts. Imax is much higher than Imin for each tube. Imin is zero, cut off. The resultant wave at common Rk becomes like a rectifier, and the Vdc content of wave becomes higher than at idle. Ia input from PSU increases bay maybe 2 times with class AB max. Ea x Ia input may be 56W, and if 30W audio PO is obtained then Pda = 26W. And if you measured the Vdc at Ek, sure enough, your meter would merely have an RC LPF to shunt the Vac at the cap to allow the measurement of Vdc, and sure enough you'd find its a lot higher than at idle. and most ripple is filtered away, lest Vac be fed to OP tube grids as well as amplified Vdc bias voltage. The rate of rise I assume is the sawtooth rise, and not the slow change to Vdc bias. But it seems to me that the negative OP tube grid bias DOES INCREASE Nope. Look at the bottom of fig 2. It does not increase, except for the 'rise time' of the 'ripple' you just 'wondered' about. But the patent says the -Vdc DOES increase, due to action I quoted " ...as the bias on the grids of the push-pull amplifier tubes becomes more negative by the control line, the plate current of these tubes is reduced to a value at which the system finds equilibrium.." The control line is the Vdc amplifier, the 6SN7. to keep the total plate current constant Wrong, as he explicitly states with what I already quoted: "the plate current rises substantially but the grid bias voltage remains substantially at it's no load value." Over a short period of time yes, but not if the input signal is continuous. The idea is to control the bias at idle with a music signal. Sine waves up to clipping with a low RLa-a for max class AB cause significant -Vdc bias change. regardless of the OP tube loading in class AB when under normal fixed bias operation, total Iadc to the OP tubes can more than double during class AB operation. And it does here too because he's created an 'automatic' FIXED BIAS scheme. Sure its fixed. But only under ideal test conditions. That's the whole POINT of the invention, as he explicitly explains in the patent: "It is the purpose of the invention to provide an amplifier which will combine the high performance characteristics of the FIXED BIAS type of amplifier, with the freedom of criticalness of the self bias form of amplifier..." (emphasis mine) yes, yes, all very well, and a waste of a 6SN7 IMHO. And there is NOTHING to combat any Idc imbalance in an OP stage. With an old Leak, there were two x 600 ohm Rk each with bypass cap. This worked magnificently while coupling caps remained good with no leakage, and tubes didn't age, but when they did age, the differences in Iadc was minimised in a way that just don't happen with a common Rk, eg, in Quad-II, and in the original Williamson. If one wanted even better Idc balance and simple bias reg then one might use Rk = 1k2, and bias both OP grids at say + 30Vdc, and Ek = +60V, for Ia in each = 50mA. Today one could use CCS to bias the cathodes. But the higher the Rk value, the larger the Ek swing due to rectifier effects when AB action happens. The conditions for the increase in negative grid bias depend on how long the high power class AB effort is sustained. Exactly no, as he says again in what I already quoted: "the grid bias voltage remains substantially at it's no load value." Ah well, Mr Walsh has fallen well short of showing informing us fully it seems. He has, or at least his attorney has got you properly bambozzled, probably on purpose so that they know what's being said, but you don't, and they wouldn't want anyone to really know, lest ppl work it out and copy it with a slight difference. We are discussing how a patent has been written and not how a scientific paper which tells all might tell it, too very different exercises. None of Walsh's wave forms show the variation in applied OP tube bias over a long period of say thousands of times the time for one wave at the test signal frequency. If the test signal is at 400Hz, a common F used for testing amps in 1947, then one might like to know what happens to grid bias voltage over a sustained 30W power level from AB 2A3 over say a 10 second time, HE TELLS YOU: "the grid bias voltage remains substantially at it's no load value." Repeating the same line like a parrot will not hide your misunderstanding of how the Brook circuit works. There is that legal word in there, "substantially", and it allows them to say almost anything, and get granted the patent. Pity help anyone building a similar thing or copying it. Then Walshie's lawyers take anyone doing similar to bits and they all get paid, and such is the nature of legals in enterprize - endless arguments over how some half baked amp circuit works, and what sales and money the owner of the patent is missing out on etc, etc, etc. So to beat Walshie's lawyers, you needed a bigger better legal team, and you needed to be rich, and basically out-legal your opposition. Meanwhile, the truth about the circuit remains obscure to just about everyone. What is missing is a graph showing the increase of -Vdc bias to OP grids against the increase in PO to an RLa-a which gives class AB action and the wave forms already shown. And on the graph the Iadc input to OPT CT and B+ at CT should also be shown. I would say I have Walsh's idea sussed, and I ain't in any hurry to copy it and I know why. and my guess is the bias applied to 2A3 would indeed go very negative, but the trace shown in the patent used to display the sawtooth shows only a tiny number of test signal waves, so you can't see the slow Vdc change. Because it's irrelevant since "the grid bias voltage remains substantially at it's no load value." Parroting makes you look a fool. So I see that this Walsh auto biasing method has the same defect of all automatic servo biasing or cathode RC network biasing of class AB tubes if the amp works in class AB, or B, and high levels are sustained. You 'see' it because you do the three monkeys, hear nothing, see nothing, speak nothing, but what you've already 'concluded'. And telling me I'm like more than one dumb monkey does nothing to show how wrong you are. But while the amp works in class A for most of the time, servo bias or cathode biasing is OK. The Walsh auto bias would work better than RC cathode biasing to maintain constant Ia in OP tubes at the idle conditioni, but for lowest THD in class AB, one needs to allow unimpeded rise in total tube Ia and NO CHANGE to all electrode voltages from the condition at idle, Which is EXACTLY what he describes in what I already quoted: "the grid bias voltage remains substantially at it's no load value." which means no fiddling with grid bias, and also means regulating the anode supply, and in 1947, the latter meant using a good choke input plate supply. That's the case with any potentiometer based fixed bias. IF B+ droops then effective 'idle' will also droop. No. The fixed bias is derived from a transformer bias winding and the winding voltage does not drop as much as the B+ might drop when producing high PO in class AB. The increase in Ia in class AB does not cause much transformer winding drop. The B+ drop comes from the effective series resistance of the choke and the rectifier tube and transformer winding resistance. Actually, Walsh's ABC control will adjust bias less negative since the minimums will decrease, reflecting the lower effective 'idle' condition but there might be a momentary higher than normal bias condition if B+ recovers faster than the ABC rise time. BS. Why don't ya see the Walsh idea used in many amps? Maybe because everyone thinks it's a 'sliding bias' due to Broskie's description. Wrong. Those who could understand the patent circuit, irrespective of what the lawyers said in print, decided it wasn't worth copying, and paying royalties, even if there were increased sales. Walsh was pushing a half baked gimick. As for 'back then', the vast majority of amplifiers were self bias because it's simpler and, hence, cheaper. Adding a tube costs money and, in addition, it was patented so they'd have to pay Walsh to use it as well. Exactly, the world sure didn't need the Walsh idea. I can't read minds but having been in product development myself I can make an educated guess they decided it wasn't 'worth it'. Precisely. I know why such a circuit would have brought smiles to faces of other amp designers, who might have said, " I shall Brook no opposition " Its not as good as Walsh makes out. Says they guy who doesn't know how it works. Says the parrot, sqawk, squawk, Screeeeaaach, I rest my case. And I buried it. R.I.P. hehe, I'm the Undead Zombie from Hell !!!!! If one uses my Dynamic Bias Stabilisation method, no Walsh type of grid voltage fiddle is attempted. Grid bias is kept constant. Cathode biasing is used, and Ek kept constant; Ek hardly rises much regardless of class AB hard work; Ia is allowed to increase as it must to maintain lowest class AB THD, so it is kept low as true fixed bias. It's certainly better than nothing but you exaggerate. Your "Dynamic Bias Stabilisation" limits the amount of shift but does not eliminate it, even if 'tweaked', because the amount of current shunted by the transistor is not 'matched' to the amount needed to maintain the idle condition 'average' current, and can't be over all Class AB conditions. Second, the point at which the transistor begins to conduct has to be an 'approximation' because it's impossible to know what the 'actual' idle current will be over tube and B+ variations. You'd be surprised how well my circuit works. Sure, there is no attempt to keep Ek **exactly** at the idle bias level when class AB action gets underway. Consider if Ea = 500V and Ik = 33mA, and Rk = 1k2 ohms. Ek at idle would be +40Vdc. Now without any shunting of Ia rise above 2 x Ia at idle during AB action, Ek might be +65Vdc at AB clipping, and grid bias of the tube is -65Vdc, and tube is biased nearly off, and lots of crossover 3H distortion appears as the wave swings through 0V at the output. But one could allow the Ek to rise to say +45Vdc with the same load without causing the huge increase in 3H. Plus you have not lost 20Vdc Ea headroom needed to get a high PO. I found that my DBS system can allow Ek to fall a bit in class AB with increasing Ia, before it rises slightly above the idle condition, so that the AB action causes the tubes to move towards more class A before moving on to being similar to class AB with fixed bias. Most music is heard in hi-fi amps with class A action only, except for drumbeats and temporary transients. The high current short term class AB peaks might slightly disturb the Ek and Idc balance in a conventional cathode bias amp, but this lurching bias effect is prevented entirely because the current that would have charged up Ck is immediately shunted by the transistors and their low collector loads. The low collector loads are not too critical, and are needed to limit the current which may be shunted through the bjt, or a mosfet if it is used. A Ck = 1,000uF charged at +40Vdc has enough charge to demolish an SS power device easily unless you have a limiting R. 100 ohms limits Ic to 0.4Amps max, easy for a BJT designed for 4 amps. You method does have the advantage of better balance due to the cathode bias (which is why I tried combining the Walsh ABC with my current balance servo). I'm not so sure. Using my DBS, you get adequate Ek reg with multiple OP tubes each with individual R&C cathode networks. The DBS has ZERO effect at idle and while the amp is in class A. One could have DBS fitted, but considerable difference in Iadc at idle. In my 300W amps, I initially tried having just 2 bjts for DBS to shunt the combined effect of 6 x 6550 on each side of the PP circuit. But more recently I thought it better to give each tubes its own TO220 bjt and R network to shunt the individual Ck. With so many OP tubes, one wants Ia fairly low in all, so that bias drift upwards won't be into a Pda danger zone. So I like Pda at idle below 1/2 max allowed Pda. Then if some tubes have Pda high and low even with RC biasing, usually their distribution won't cause significant Idc im-balance, the sum of Ia on each side will more or less balance. I found this even with only 6 OP tubes. I've also found that with GOSS cores with high max µ when lams are fully interleaved, there is tendency for core saturation to occur all too easily with VLF signals and DC imbalances. So a µ = 17,000 like some GOSS lams is BS, as it is with a toroidal OPT where the lack of a gap means µ can be 40,000, and Idc balance is critical. The answer to this bother is to hace max µ no more than about 2,500, quite enough to always get enough Lp if one follows my OPT design criteria, which most makers find amusing. To get a µ from 17,000 down to 2,500 means partial air gapping, and E&I are not interleaved maximally. Then Idc imbalance causes much less bothers, and the OPT remains an unsaturated inductance dow to a lower F at high signal levels, which is what everyone wants, or should be aware that they want. Having a non- oriented Si steel in the core is not so bad if you have huge enough cores, as µ rarely is above 3,500 max. Personally, I think balance is more important but don't think 'bias stabilization' is necessary for Class AB (as long as there's enough Class A), so I normally do cathode bias (most commonly with my current mirror balance). Class AB2 is another matter and that's what his ABC was designed for. Note that grid currents are of no consequence because they occur at the Ia peaks and he's detecting the (sum of both tubes) minimum. Why is "class AB2 another matter" ? Well, one might set up a pair of 6L6 to make a pure 12 watts in class A TRIODE with the RLa-a which allows this. Maybe 10k0. Then if RLa-a is halved, maybe you get 20W class AB1, 5k0. But if you fit two CF driver triodes you might get 33Watts in AB2, about the same as beam tetrode mode for the same tubes. Cathode waves and currents will be similar. The average Vdc at a common Rk just goes higher the more you push the tubes with a low RLa-a. For balance with just two OP tubes I prefer to use a pair of LED and an adjust pot to indicate bias balance. Owners can see their amp is OK from across the room, and can just twiddle a slot in a trim-pot at the amp front with a thumb nail gain bias balance. If they can't swing the pot far enough to get balance, one of the two tubes is stuffed. See my 5050 circuit for details - goes back to 1998, when I had made only about 4 amps up to that time, but had repaired so many with biasing troubles. The penny has been dropped a long while. Patrick Turner. |
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#19
Posted to rec.audio.tubes
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Brook 10C's
"Patrick Turner" wrote in message ... The only way to fix the auto cathode bias and keep it fixed during class AB is to shunt excessive load currents as they occur to prevent Vdc rise at cathodes. See my circuits for Dynamic Bias Stabilisation at http://www.turneraudio.com.au/300w-5...tabilizer.html This wasn't really possible in 1947, but had it been, some bright ******* would have invented it and tried to sell amps because they had it and others didn't. I need to admit, Brook's circuit is much smarter and elegant than yours. The "trough-detector" is really a smart idea, as opposed to your peak clipper.. Your circuit is bad as it introduces "transistor" distortion. At low signal, in your circuit, when the cathode current does not exceed 65mA and the transistors are off, the tube transconductance is effectively degenerated by your 10R current sensing resistors. With high-gm tubes as EL34, this degeneration is about 8%. Now, when the cathode current exceeds 65mA and the NPNs start conducting, voltage across 10R resistors stops to raise further -- 10R differential resistance becomes close to zero, thus degeneration ceases, and the tube(s) start to work as if with purely grounded (AC-wise) cathodes -- with full, not degenerated transconductance. In other words, as the current rises, you additionally increase tube transconductance by 8% on top of its natural rise caused by the law of 1.5. The WORST thing is that the transistors cut in very sharply, making this 8% transconductance modulation distortion harsh, in a "transistor-like" fashion. It is like a kink on the Vg-Ia plot. You introduce high-order distortion killing pretty much the only (debatable) advantage of tube amps -- low order distortion. Regards, Alex |
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#20
Posted to rec.audio.tubes
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Brook 10C's
On Oct 17, 10:43*pm, "Alex Pogossov" wrote:
"Patrick Turner" wrote in message ... The only way to fix the auto cathode bias and keep it fixed during class AB is to shunt excessive load currents as they occur to prevent Vdc rise at cathodes. See my circuits for Dynamic Bias Stabilisation athttp://www.turneraudio.com.au/300w-5-bias-stabilizer.html This wasn't really possible in 1947, but had it been, some bright ******* would have invented it and tried to sell amps because they had it and others didn't. I need to admit, Brook's circuit is much smarter and elegant than yours. The "trough-detector" is really a smart idea, as opposed to your peak clipper... The Brook circuit is NOT a "trough detector". The circuit detects and amplifies the change in Average Vdc across the current sensing 15r, and as this increases during class AB action, neg bias to 2A3s is increased and the Ia feed to 2A3 is reduced, forcing the 2A3 to work more like a class B amp. But while in class A or at idle, Vdc at 15r stays fairly constant, and thus Idc to the pair of 2A3s is held constant, and any other suitable tubes such as 300B may also be used. If one didn't like the increase in neg bias with heavy class AB PO, then the voltage rise at 15r could be limited to say +1.8V by having say 3 x series IN4004 across the 15r. Your circuit is bad as it introduces "transistor" distortion. At low signal, in your circuit, when the cathode current does not exceed 65mA and the transistors are off, the tube transconductance is effectively degenerated by your 10R current sensing resistors. You have not tried my circuit, nor measured it, and you have no clue what your'e talking about. The transistors only begin to conduct Ia when the amp moves into class AB from class A. The transistors are completely unoperative during class A operation, thus don't cause any additional THD to that naturally generated. The amount of distortion generated by the transistors at highest levels into the lowest RLa-a at say 300+ watts is MUCH LESS than what is generated by the circuit without the bjt "current shunters", and NO MORE or spectrally worse than pure fixed bias and the DBS acts to enable a PP cathode biased amp to perform just like a fixed bias amp. So before you tell me my circuit generates a pile of ****ful distortions, please aquaint yourself with the facts. Did ya think I was born yesterday? Did ya think I would not have tested the DBS exhaustively before giving the idea to the world? And for Free. With high-gm tubes as EL34, this degeneration is about 8%. Now, when the cathode current exceeds 65mA and the NPNs start conducting, voltage across 10R resistors stops to raise further -- 10R differential resistance becomes close to zero, thus degeneration ceases, and the tube(s) start to work as if with purely grounded (AC-wise) cathodes -- with full, not degenerated transconductance. The signal across the 10r Ia sensors is clipped by the Ia active shunting of what is otherwise going to charge up the large value Cks. There is virtually no effect to increase THD. In other words, as the current rises, you additionally increase tube transconductance by 8% on top of its natural rise caused by the law of 1.5. Bull****. The WORST thing is that the transistors cut in very sharply, making this 8% transconductance modulation distortion harsh, in a "transistor-like" fashion. It is like a kink on the Vg-Ia plot. You introduce high-order distortion killing pretty much the only (debatable) advantage of tube amps -- low order distortion. You cannot understand something very simple. The bjts merely shunt the excessive Ia as it tries to charge up the Cks, and thus Ek is held low. There is virtually no interfering signal across Ck injected into the signal path. The action of the bjts is buffered by the collector R and the turn on behaviour of the bjts complements the savage turn-on and turn-off behaviour of the tubes. When you consider just how frightfully the Ia change in class AB tub operation is, with say 40% THD in Ia, the presence of the bjts contributes virtually nothing extra. So, my circuit measures just as well as a fixed bias class AB amp, so you need to try the circuit out before telling me as you so often have that what I do is "bad". Despite the 40% THD in tube currents in class AB amps, the result gives very much lower THD after the summing of the currents in the PP circuit, and without any FB at all anywhere, typical high PO AB1 with fixed bias UL gives 3% THD at Vo. Lots of harmonics are produced by the switching action of the tubes, and I could not identify any significant additional harmonics attributable to the DBS. With cathode biasing without DBS, maybe its 10% at the same PO, because Ek has doubled with a continuous sine wave test signal. But with DBS, and 20% local CFB, the THD is a heck of a lot lower. The BJTs in all my amp circuits act as compliant slaves to tubes - willing servants who allow the tubes to get on better with their purpose in life and without interference. The tubes run the ship and manage the needs of the passengers, the transistors clean the toilets and shovel the coal. Have you got a better idea? I've seen so many BS claims made about bias servo circuits. Very few work properly. Patrick Turner. Regards, Alex |
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#21
Posted to rec.audio.tubes
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Brook 10C's
On Oct 18, 1:56*am, flipper wrote:
On Mon, 17 Oct 2011 22:43:59 +1100, "Alex Pogossov" wrote: "Patrick Turner" wrote in message .... The only way to fix the auto cathode bias and keep it fixed during class AB is to shunt excessive load currents as they occur to prevent Vdc rise at cathodes. See my circuits for Dynamic Bias Stabilisation athttp://www.turneraudio.com.au/300w-5-bias-stabilizer.html This wasn't really possible in 1947, but had it been, some bright ******* would have invented it and tried to sell amps because they had it and others didn't. I need to admit, Brook's circuit is much smarter and elegant than yours. The "trough-detector" is really a smart idea, as opposed to your peak clipper.. Your circuit is bad as it introduces "transistor" distortion. At low signal, in your circuit, when the cathode current does not exceed 65mA and the transistors are off, the tube transconductance is effectively degenerated by your 10R current sensing resistors. With high-gm tubes as EL34, this degeneration is about 8%. Now, when the cathode current exceeds 65mA and the NPNs start conducting, voltage across 10R resistors stops to raise further -- 10R differential resistance becomes close to zero, thus degeneration ceases, and the tube(s) start to work as if with purely grounded (AC-wise) cathodes -- with full, not degenerated transconductance. In other words, as the current rises, you additionally increase tube transconductance by 8% on top of its natural rise caused by the law of 1..5. The WORST thing is that the transistors cut in very sharply, making this 8% transconductance modulation distortion harsh, in a "transistor-like" fashion. It is like a kink on the Vg-Ia plot. You introduce high-order distortion killing pretty much the only (debatable) advantage of tube amps -- low order distortion. Regards, Alex I see your point but think there's a detail missing. Degeneration changes from 10 ohm not to 0 but 47 ohm (through the transistor). The essence of your point remains, just maybe not in the same polarity. I'm not so sure the transistor turn on is quite as 'sharp' as you imply, though. The Vbe curve seems 'small' by comparison to the tube, for sure, but the voltage across the 10 ohm is rather small as well. The BJT turn on behaviour is no worse than a tube's. Hard to tell exactly what it would look like by just peering at the circuit because there's negative feedback there. I.E. As the transistor turns on and sinks current the sense resistor voltage increase is less than 'normal' because part of the current that would otherwise flow through it is diverted to the 47 Ohm bypass. In class AB, What is seen across the Ck is LESS sawtooth charging signal, as the peak current is shunted. What is seen across the 10 ohms is a square wave instead of rectifier type waves with massive % THD. It's also worth noting there is already a gain change as the plate load drops when the other tube goes into cutoff and is no longer driving it's half of the primary This is normal behaviour in all class AB circuits. Tetrodes and pentodes in AB have the sharpest switching and generate the worst 3H, 5H and 7H as a result when RLa changes from 1/2 RLa-a in class A to 1/4 RLa in class B above the class A working. UL has less sharp cut off behvaiour, and Triode the least sharp. With 20% CFB, the tubes are also working like 20% UL with FB, so THD is much less than plain pure tetrode or pentode. The DBS does not make things any worse, and in fact it stops all bias "lurching about" from transients reaching above the class A -AB threshold. The more closely you examine class AB operation, the worse it looks, but in fact there are many excellent sounding class AB amps around, and the use of DBS does not one bit of harm to the sound at all. DBS allows me to have 12 output tubes with simple cathode bias, and avoid having 12 adjust pots for fixed bias. I don't like high bias currents. 35mA is plenty with 6550 etc. The CFB allows Eg2 lower than Ea and so Ek is lower than if Eg2 = Ea. So Rk need not be low value and get hot. And yet I find that Rk may be 1/2 what might be used and still there is adequate reg of bias, and an additional truly fixed neg bias may be applied. I have adequate protection measures against any bias failure of one or more OP tubes. Of course it isn't perfect, because when the amp shuts down after one tube spits the dummy, nobody knows which one it is. I've not had any orders for 300W amps for 5 years, and the pair I have are still a work in progress, and I may indeed include a circuit which tells me which tube of the 12 has spat its dummy. It means yet another little circuit board and 12 LEDs and SCRs to control each one so that when amp shut down occurs because a faulty tube conducting too much Ia, an LED lights up for that tube and that one only. It then allows an owner to pull that tube out, plug a new one in, and the amp should then work fine without a tech being needed, or sending amps to be serviced, which is a huge expense when the amps weigh 100Kg in 4 chassis. I like user friendly tube amps which don't cost much to keep on the road. Many other brands like ARC and Manley Labs and most Chinese mades are all ****ing attrocious in regard to active protection and biasing methods. Patrick Turner. |
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#22
Posted to rec.audio.tubes
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Brook 10C's
There is no "Vdc" in Class AB. It's a friggin 'rectified AC waveform', as you once described it. Unfortunately, you cannot recognise where there is a Vdc present as you are blinded by the Vac shown at the top of the 15 ohms. "The Vac shown at the top of the 15 ohm" is not a "Vdc." That's why you were forced to call it Vac in your babble. The voltage across the 15 ohms is **always** above 0V. It **cannot go negative**, OK, Yes, 'ok', and you can calculate an average but the waveform is not 'DC'. There is a Vdc component of the signal across the 15r. You fail to understand this simple concept. The DC amp following the 15r reacts as though there is a change in Vdc across the 15r. and the voltage across the 15 ohms pilot sensing resistance is caused by both the AC current constituent and the DC current constituent. A convenient mathematical construct which does not alter the fact the waveform is a waveform and is not a DC signal. I'm not going to let you call me a parrot if I repeat myself. You either get it, or you don't, and if you don't, then fine, I'll let you stay with what I think you don't get. When the amp works in class AB with a low load to allow 30W, the positive going Vac peaks at 15 ohms are several times the Vdc found at idle with no signal. Yep. Conveniently, the minimums of the waveform are 2x idle so if we detect those we can capture and hold the same value as would be there when at idle (when it actually is DC). "If" is just a word. To properly detect the troughs in the waves at 15r, one needs to have a diode cathode connected to 15r, with its anode to a cap and an R taken up to a + rail. The Vdc across the C to 0V will be equal to diode voltage drop plus the bias Idc x 15r. Vdc across C to 0V is a positive Vdc, and is then governed by the bias and negative going peaks of any Vac at 15r. So such a recovered voltage could be used to work a a Vdc amp to adjust bias. The best rectifier diode to use would be a silicon one with very low but very predictable and small Vdc forward voltage drop. The Walsh patent is entirely bamboozling, and probably meant to be that way. Many possible test results are completely missing. Pity help anyone who made something similar but didn't realise they were copying it. But never mind that, just a side issue about USA business practices, often very tricky when it comes to patents. Look how long Deforest and Armstrong argued in the ****ing courts. I still don't think you understand this Brook circuit you are trying to discuss, and only by building it and testing is will you get it, IMHO. I've read the rest of your reply, but see no point in continuing to argue. Patrick Turner. |
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#23
Posted to rec.audio.tubes
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Brook 10C's
"flipper" wrote in message ... On Mon, 17 Oct 2011 22:43:59 +1100, "Alex Pogossov" wrote: "Patrick Turner" wrote in message ... The only way to fix the auto cathode bias and keep it fixed during class AB is to shunt excessive load currents as they occur to prevent Vdc rise at cathodes. See my circuits for Dynamic Bias Stabilisation at http://www.turneraudio.com.au/300w-5...tabilizer.html This wasn't really possible in 1947, but had it been, some bright ******* would have invented it and tried to sell amps because they had it and others didn't. I need to admit, Brook's circuit is much smarter and elegant than yours. The "trough-detector" is really a smart idea, as opposed to your peak clipper.. Your circuit is bad as it introduces "transistor" distortion. At low signal, in your circuit, when the cathode current does not exceed 65mA and the transistors are off, the tube transconductance is effectively degenerated by your 10R current sensing resistors. With high-gm tubes as EL34, this degeneration is about 8%. Now, when the cathode current exceeds 65mA and the NPNs start conducting, voltage across 10R resistors stops to raise further -- 10R differential resistance becomes close to zero, thus degeneration ceases, and the tube(s) start to work as if with purely grounded (AC-wise) cathodes -- with full, not degenerated transconductance. In other words, as the current rises, you additionally increase tube transconductance by 8% on top of its natural rise caused by the law of 1.5. The WORST thing is that the transistors cut in very sharply, making this 8% transconductance modulation distortion harsh, in a "transistor-like" fashion. It is like a kink on the Vg-Ia plot. You introduce high-order distortion killing pretty much the only (debatable) advantage of tube amps -- low order distortion. Regards, Alex I see your point but think there's a detail missing. Degeneration changes from 10 ohm not to 0 but 47 ohm (through the transistor). The essence of your point remains, just maybe not in the same polarity. I'm not so sure the transistor turn on is quite as 'sharp' as you imply, though. The Vbe curve seems 'small' by comparison to the tube, for sure, but the voltage across the 10 ohm is rather small as well. Hard to tell exactly what it would look like by just peering at the circuit because there's negative feedback there. I.E. As the transistor turns on and sinks current the sense resistor voltage increase is less than 'normal' because part of the current that would otherwise flow through it is diverted to the 47 Ohm bypass. It's also worth noting there is already a gain change as the plate load drops when the other tube goes into cutoff and is no longer driving it's half of the primary. The 47R resistors in the collectors do not do anything because the transistors are not going into saturation. I do not know why these 47R resistirs are there. But I overlooked 1K resistors in series with the bases. These indeed soften the transistor opening. Assuming typical beta=100, these 1Ks translate into virtual 10R in series with the emitters. That means that from 10R degeneration under 65mA it goes to about 5R degeneration above 65mA. Only 4% net transconduction variation. Yet it is crazy to mix distortion current, created by the exponential curve of the transistor, into the cathodes of the "smooth" tubes. |
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#24
Posted to rec.audio.tubes
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Brook 10C's
The 47R resistors in the collectors do not do anything because the transistors are not going into saturation. I do not know why these 47R resistirs are there. Transistors need to be protected from themselves and unless collector resistors are added to my circuit, along with series base resistors, they can run away with enthusiasm and short circuit themselves to death in less time you can say beejaytee. Too be SURE the collector current is never more than Ek / 47 ohms, the 47 ohms are used. Its not a critical value. But I overlooked 1K resistors in series with the bases. These indeed soften the transistor opening. Yes, indeed.....The angel or the devil is always in the detail..... Assuming typical beta=100, these 1Ks translate into virtual 10R in series with the emitters. What makes you think beta = 100? most power transistors might be less. But it ain't critical, because the local NFB around the bjt circuit means that while ever Ik peak remains high enough to turn on the bjts, they conduct, and they cease conduction when they don't have to....., or more if they do have to, until the job is done. That means that from 10R degeneration under 65mA it goes to about 5R degeneration above 65mA. Only 4% net transconduction variation. Yet it is crazy to mix distortion current, created by the exponential curve of the transistor, into the cathodes of *the "smooth" tubes.- Nah, you are always seeing craziness in other blokes' attitudes when in fact they might be a whole lot more sensible than you are. The tube **current** in AB amps has HUGE THD, but the bjts hardly make any difference whatsoever. I suggest you spend 30 minutes converting an amp you have laying around so that it works like mine, you'll be very happy, and wonder why you were so negative. I've used DBS in a recently re-engineered pair of Quad-II amps and I'm getting 32 Watts of very clean power with a continuous sine wave and THD is far less than without DBS. The owner finds his Quads beat the pants off all the other amps he's got. The only critical part of the circuit is the current sensing R value, and what ya want is Ek to stay level. If Rsensor is too large, Ek reduces as PO is raised above 0V and this indicates bjts are turning on too early, and if Rsensor is too small, Ek rises too much and isn't reduced enough at clipping with low RLa-a. When its just right, Ek stays level for all class A, then rises no more than 10% at clipping with a low RLa-a. I am presently completely re-wiring a pair of Quad-II-Forty because dear old Andy Grove and the Chinese wannabe amp makers didn't quite get things right. If one connects 4 ohms across the highest output labelled for 8 ohms, and runs the amps to clipping with a continuous sine wave, Ek moves from +40Vdc to +58Vdc with Rk at 470 ohms, a more sensible value than the original 390 ohms. This could nearly all be stopped with dBS, but this time there isn't any real need. The Quad- II-40 have 4 ohm outlets, and use of 4 ohms gives 37Watts and music at average values of 4 watts won't cause Ek to move very much. Original Quad-II don't have a proper 4 ohm strapping, although the original OPTs **can be removed from pots** and secs re-strapped to give the extra terminal setting so that RLa-a = 4k0 when 4 ohms is used, not ****ing 2k0 when ppl connect 4 ohms to the Quad-II when strapped for 8 ohms, as many ppl do. And while we are on the subject of Brook 10C, Our Dear Flipper maintains that there is no Vdc change across the 15r common Rk for a pair of 2A3, when they have to power a low RLa-a to make 30W with a continuous sine wave. But when I tested the second of the 2 Quad-II 40 amps I've been reforming, I found that I get about 0.16Vdc across the winding resistance of the 1/2 cathode feeback winding at idle. With class AB and a low RLa-a, I found Vdc aross the windings to rise to 0.221Vdc quite easily. The change in Vdc = 0.6Vdc approx, and if applied to am inverting VDC amp with gain of 200 x like a cascaded 6SN7, a la Brook, then the change in bias could be -120Vdc. Flipper says no such thing could occur, and I say it could, but hey, I'll go my way, he can go his, in peace, and The Whirled can decide who is correct. I'm not here to win arguments, I'm here to explain what I do and invite others to try, but they sure don't have to. Maybe they have better ways of doing stuff. I can't know everything. Patrick Turner. |
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#25
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Brook 10C's
On Oct 19, 2:48*pm, flipper wrote:
On Tue, 18 Oct 2011 22:01:43 +1100, "Alex Pogossov" wrote: "flipper" wrote in message .. . On Mon, 17 Oct 2011 22:43:59 +1100, "Alex Pogossov" wrote: "Patrick Turner" wrote in message .... The only way to fix the auto cathode bias and keep it fixed during class AB is to shunt excessive load currents as they occur to prevent Vdc rise at cathodes. See my circuits for Dynamic Bias Stabilisation athttp://www.turneraudio.com.au/300w-5-bias-stabilizer.html This wasn't really possible in 1947, but had it been, some bright ******* would have invented it and tried to sell amps because they had it and others didn't. I need to admit, Brook's circuit is much smarter and elegant than yours. The "trough-detector" is really a smart idea, as opposed to your peak clipper.. Your circuit is bad as it introduces "transistor" distortion. At low signal, in your circuit, when the cathode current does not exceed 65mA and the transistors are off, the tube transconductance is effectively degenerated by your 10R current sensing resistors. With high-gm tubes as EL34, this degeneration is about 8%. Now, when the cathode current exceeds 65mA and the NPNs start conducting, voltage across 10R resistors stops to raise further -- 10R differential resistance becomes close to zero, thus degeneration ceases, and the tube(s) start to work as if with purely grounded (AC-wise) cathodes -- with full, not degenerated transconductance. In other words, as the current rises, you additionally increase tube transconductance by 8% on top of its natural rise caused by the law of 1.5. The WORST thing is that the transistors cut in very sharply, making this 8% transconductance modulation distortion harsh, in a "transistor-like" fashion. It is like a kink on the Vg-Ia plot. You introduce high-order distortion killing pretty much the only (debatable) advantage of tube amps -- low order distortion. Regards, Alex I see your point but think there's a detail missing. Degeneration changes from 10 ohm not to 0 but 47 ohm (through the transistor). The essence of your point remains, just maybe not in the same polarity. I'm not so sure the transistor turn on is quite as 'sharp' as you imply, though. The Vbe curve seems 'small' by comparison to the tube, for sure, but the voltage across the 10 ohm is rather small as well. Hard to tell exactly what it would look like by just peering at the circuit because there's negative feedback there. I.E. As the transistor turns on and sinks current the sense resistor voltage increase is less than 'normal' because part of the current that would otherwise flow through it is diverted to the 47 Ohm bypass. It's also worth noting there is already a gain change as the plate load drops when the other tube goes into cutoff and is no longer driving it's half of the primary. The 47R resistors in the collectors do not do anything because the transistors are not going into saturation. I do not know why these 47R resistirs are there. Yeah, I missed the saturation point. But I overlooked 1K resistors in series with the bases. These indeed soften the transistor opening. Assuming typical beta=100, these 1Ks translate into virtual 10R in series with the emitters. That means that from 10R degeneration under 65mA it goes to about 5R degeneration above 65mA. Only 4% net transconduction variation. Sounds about right. Yet it is crazy to mix distortion current, created by the exponential curve of the transistor, into the cathodes of *the "smooth" tubes. Well, I would imagine the logic is it's better than going into Class C but I think that is better dealt with by taking advantage of nominal program level being significantly lower than peak and designing in sufficient Class A. Amps with DBS can still be pushed well into class C. All the DBS does is stop the Ek rising during class AB1 as it does, well before grid current begins to flow to charge up the coupling caps. I don't bother building class AB2 amps; I see no reason, and if ppl want higher PO than 2 tubes provide in AB1, I humbly fukkin suggest they use more OP tubes, and desist from whipping the 2 horses to make them pull ever heavier loads. The DBS makes the amp act like a fixed bias amp, and in a hi-fi situation, its doubtful more PO is wanted than AB1 can provide because AB1 RLa-a is fairly high, and usually higher than RLa-a for a PA amp where high PO is needed to wow ppl in a rock'n'roll venue. Patrick Turner. That. btw, was part of the transistor amp 'spec wars' back in the day since, with the traditional complimentary pair, they could claim 'RMS' power to the rails but a typical Class AB (cathode bias) tube amp can't. The transistor amp 'specs' better but it's of little consequence in practice. Then the Japanese invented "PPMO" and lord only knows how that's calculated. Something like how much power the supply caps can deliver over 1mS, or some such nonsense.- Hide quoted text - - Show quoted text - |
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#26
Posted to rec.audio.tubes
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Brook 10C's
"Patrick Turner" wrote in message ... The 47R resistors in the collectors do not do anything because the transistors are not going into saturation. I do not know why these 47R resistirs are there. Transistors need to be protected from themselves and unless collector resistors are added to my circuit, along with series base resistors, they can run away with enthusiasm and short circuit themselves to death in less time you can say beejaytee. Too be SURE the collector current is never more than Ek / 47 ohms, the 47 ohms are used. Its not a critical value. But I overlooked 1K resistors in series with the bases. These indeed soften the transistor opening. Yes, indeed.....The angel or the devil is always in the detail..... Assuming typical beta=100, these 1Ks translate into virtual 10R in series with the emitters. What makes you think beta = 100? most power transistors might be less. But it ain't critical, because the local NFB around the bjt circuit means that while ever Ik peak remains high enough to turn on the bjts, they conduct, and they cease conduction when they don't have to....., or more if they do have to, until the job is done. That means that from 10R degeneration under 65mA it goes to about 5R degeneration above 65mA. Only 4% net transconduction variation. Yet it is crazy to mix distortion current, created by the exponential curve of the transistor, into the cathodes of the "smooth" tubes.- Nah, you are always seeing craziness in other blokes' attitudes when in fact they might be a whole lot more sensible than you are. The tube **current** in AB amps has HUGE THD, but the bjts hardly make any difference whatsoever. I suggest you spend 30 minutes converting an amp you have laying around so that it works like mine, you'll be very happy, and wonder why you were so negative. Alex: I just see illogical to add transistor distortion to valve amps. If you used say 1R current sensing resistors instead of 10R and x10 op-amp gain stage before the base of the shunting transistor, I would consider it a "better" solution. Have you done the following experiment. While your amp is idling or playing, intermittently short one of your 10R sensing resistors to ground. Will you hear some crackling, even soft, not loud? If yes, then it is the amount of "transistor-like" distortion which your circuit mixes in. (You can argue that inherent THD is much greater, and/or masked by the loud musical material, etc., but then why build tube amps at all?) Or perhaps you will not hear any crackling from that experiment -- maybe your NFB absorbs it. Then -- congratulations -- you "won" the argument. |
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#27
Posted to rec.audio.tubes
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Brook 10C's
On Sun, 16 Oct 2011 02:56:11 -0700 (PDT), Patrick Turner wrote: Bose has a "Lifestyle System". But tiny crummy 2" drivers in matchbox speakers are on ceiling with bass speaker in corner, and kitchen remote. Shiealas fall for such crap, but not me. I remember selling the 901's in hi-fi stores, all 8 4.sumthing" spkrs that sound "..best.." if placed into a corner. I sold alot of them got a good spiff off it. Sound sucxd. Then Bose packaged the whole thing AGAIN (with a rack mount 'eq' box) for P.A. work. They sold a **** load of them, that sort of did the job. They made a great rack mount power amp (1800?) at the time. Remember, the Bose 'mountain' is a mountain of piled garbage the city almost gave to Bose to build the 1st buildings. Sort of fits, huh? Although, I have to say the new'ish Bose poles do the job in the right room, for a small 3p band. A friend did promo for Bose over the guitar version..ok for acoustic..nothing more. B&O make a range of truly horrid products. I've had to work on their POSs. Quad amps could have been better. I have bullet holes still healing up after the last time I said that here. In the MI world, Sound City, Vox, and 80% of the other Icon amp companies also made pure bull**** crap. Hiwatt has made '****'. Wanna talk Marshall blunders.. WOAH.. 2 shy 2 spy.. (pun) Really. But yeah, ya always get some one who has to defend their fave rave name. Also, sometimes the fact that they are (in this case) 'UK' designed/built makes some of them neat.. SS Thomas Organ Vox is great for what it is. ALL product could of been better. I happen to like Quad. : ... But ESL57 were exceptionally good, and I'd hazard a guess the Brook 10C with 300B would be good to drive ESL57 - if you can ever find a pair that work properly after 40 years and which won't cook an amp as I have seen them do when arcing occurs in old panels. "..If I ruled the world..everyday would be the 1st day of spring.." JJTj "..As I leaned over to correct her spelling of the words: "..Boogie-Woogie..", I realized I loved her.." |
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#28
Posted to rec.audio.tubes
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Brook 10C's
Shiealas fall for such crap, but not me. The Bose 'eq' system made the buyer desire the spkr. The "..high tech.." of the spkr sold it to the snobs that could, and were, sold anything some other idiot told them was neat & swifty. Here in MA, the Havard Sq area was all around tons of students who wanted to believe anything they were told. The desire for Hi-Fi was deafening. Tech Hi-Fi, Atlantis Sound (where I worked) and other stores were everywhere. One was a McIntosh *ONLY* store that lasted a long long time. But anyway..dig this: At the Atlantis Sound store I was at, we had a box on the push button spkr selector that was a 'suck' control. ANY spkr for sale could be made to sound worse then the one 'ON' sale. And we had a 'shooter' that could sound better then ANYTHING even with the 'suck' control on. $800 a pair, Pioneer 4 way 'studio' thing with weird LP guts, foam woofer & more. Wish I had a pair. We once offered a 24 hr special. Bring in anything and we will give 200% of the price off the '..list.." price of your system. We had people bring in beer, pizza, weed, guitars, and more, and sold a ****load of Hi-Fi for MORE $ because the list prices were so high, and kept all the beer, etc, and gave the pizza to charity. We also sold Crown reel 2 reel. Some weird brands, and we were paid well. AH, the Atlantis stories.. Only one regret... I still have a B&Blue mark on my ass from this. As employee, I was allowed to use anything that was in inventory at home. SHEI-T, I had (by then numbers) $14k of gear at home. When the Worc store closed, I was one of only 2 who returned the stuff. 2 Days later, I learn there was never a paper trail, no one cared, Duh? ----- Anyone else remember the phono cartridge boogie? Atlantis had major $$ involved in ADC. They sold it by the buckets. If we could get the rube to 'upgrade' to a diff color needle, we got 40-70% more spiff. All the needles were the same, just diff color holders.. Bose spiffe'd me $10 every 901 sold. CVega $1-5. Other then that, the Wiz paid me. Ken, da Wiz, would show up every now and then, and play price god. We'd have a rube with cash in hand about to hand US said cash, all happy, and Ken would tap the rube with his wand (he carried it,wore bent hat, cloak, etc) and 'poof', lowered the price $100. And it came out of MY spiff..not his. ...yup..bored, online, and Bose Bashing... JJTj You know those Kix just keep getting harder to find.. ....and Frosted Flakes ain't giving you peace of mind.. You better chow down more Bran cakes, now.. ...and get yer ass straight... |
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#29
Posted to rec.audio.tubes
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Brook 10C's
On Oct 21, 2:53*pm, flipper wrote:
On Wed, 19 Oct 2011 01:02:54 -0700 (PDT), Patrick Turner wrote: snip And while we are on the subject of Brook 10C, Our Dear Flipper maintains that there is no Vdc change across the 15r common Rk for a pair of 2A3, when they have to power a low RLa-a to make 30W with a continuous sine wave. I never said any such thing. Not exactly, but indirectly, because you seem to be insisting that a change in Vdc at the DC amp output remains unchanged because of that stuff about time constants, and trough detection going on, and the Vac across the 15r, But my knowledge tells me that where you measure a Vdc rise in 15r regardless of the Vac there, that Vdc rise will have dramatic effects on the bias applied to 2A3 when it is amplified about 200 times. I could be wrong though, and I'll just have to build & measure something myself. Until then, you'll just have to tolerate me having an opposite opinion, and I'm sure your world won't fall to bits as a result. In fact YOU do because you claim the DC amp will change bias to KEEP Ek 'Vdc' constant, and never mind that the inventor explicitly says bias does NOT change because you've arbitrarily pulled from thin air they're all 'lying'. I thought I quoted where Walsh he says the negative bias does increase and a state of equilibrium was reached. Maybe you missed that in the patent. Anyway, I tire quickly of arguments these days. If you'd ever read the patent trying to see how it's intended to work rather than looking for snippets to 'support' your preconceived notions you'd see he specifies how the 'detector' tube should be biased, namely the Rk and plate loading should be selected so that, at idle, plate voltage rests at mu times Ek. Unfortunately my tube models are not accurate at very low plate voltages (something I've run into before) but adjusting things to meet his criteria I have successfully modeled the 6SN7 'detector' so that it holds plate voltage within .4V of 80mA idle with peak currents through Rk corresponding to what you call 'Vdc' equivalent to a 190mA average. If, however, I put a 190mA idle, creating an *actual DC* "Vdc" of 2.87V (vs the 1.2V 80mA idle) plate shifts 8.8V, which is close to 20 times the shift when it's 'AC'. I don't use modelling. It proves nothing to me; ya gotta build something and measure it. I also managed to model it using a 6DJ8. In short, it works if you properly bias the tube Well, something might work, do something or other, not 100% sure what, and is see very little difference between the Brook 10C bias amp and using a cap across the 15r, so that if all the Vdc change is nearly captured at that point, then you have a Vdc amp to sample what Vdc you want, so that 2A3 bias can be much increased to reduce the Idc input during heavy class AB working. I'm saying that reducing Idc to the OPT CT by biasing grids more negative puts the tubes into class B conditions and there's a huge THD rise. One might only need 1 x MJE 350 with Re to give the same gain as the cascaded 6SN7, and the wanted and the wanted Vdc inversion to make bias more negative for OP tubes. But I won't be employing any such circuit any time soon. Nobody else seems to want to use the Brook idea either. Patrick Turner. |
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#30
Posted to rec.audio.tubes
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Brook 10C's
I still don't think you understand this Brook circuit you are trying
to discuss, and only by building it and testing is will you get it, IMHO. So build one so you can understand it. I've read the rest of your reply, but see no point in continuing to argue. Wise choice since I have a filed and approved patent plus a manufactured and sold device based on the same principle to back up my position. That you take the word of somebody or anybody who patented an ampifier gimick shows you lack the ability to have doubts, and to ever think that you could ever be wrong. All things claimed by a train full of people still need validation on your workbench. Words in patents and your modelling are NOT reality. Many ppl can be wrong about an idea, even though it seems so right. When Challenger fell from the sky, had not a huge certainty been established about the integrity of the Shuttle? But the fukkin thing still went wrong, and engineers had to re-assess. So when you jump up an down in triumph because you have concluded I'm wrong, the world will just think your'e a dumb jerk. You have to work a lot harder at proving you are right. I've got so much paid work I don't have time to build Brook's idea, so I don't much care if I lose this argument. I don't like Brook's idea. Having a cascaded 6SN7 to control bias could lead to smoke; if the tube ever fails, or the negative supply fails, watch out. I can't think of very many ppl who have included Vdc amps in their tube amp schematics; most bean counters always said no anyway. Patrick Turner. |
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#31
Posted to rec.audio.tubes
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Brook 10C's
The last current bid was $17,800, bidding had ended, and and the reserve not met. I'd have given $100 each for such old boatanchor junk, knowing one would have to gut them entirely and re-build them. The IST is not a potted tranny, merely a bell ended thinge. OPT and PT are not potted, and look like Old Hammonds, and a bit rusty. New PSU caps have been placed badly on the chassis leaving two big holes where old style electros were used. Wiring under the chassis is a complete rat's nest, and has probably been repaired/modified umpteen times. There are no 2A3 to be seen anywhere. These are very ordinary old crappy amps. But of course some ppl think they are worth $18,000, and its a just another reminder of how stupid the world is. I guess some ppl think a worn out 1955 Ford or 1955 bicycle might be worth the same money. Patrick Turner. Actually Patrick, you are wrong. They were the best amplifiers of their day, their appearance aside. A great deal of care was taken in the winding of their transformers. They were wildly bettter than anything else in their day for low insertion loss and perfect AC and DC symmetry, and were capable of distortion performance unmatched until the latest generation of tube amps, and with much less feedback. The driver circuitry is well worth studying on all Brook amps. Brook failed for several reasons, but one was the pedestrian appearance of their sets, as opposed to the chrome and black of McIntosh and the Marantz brown. Another was their low power output as compared to the competition. It's worth noting, that until the very late 1950s or early 60s, no commercial manufacturer COULD use WE 300x (A,B are actually identical except for a pin on the base which no one ever used!) tubes for consumer sale. The WE tubes were not LICENSED for that use. There was a huge pool of patents the tube manufacturers shared. WE was part of that pool and the agreement was that the others were licensed for consumer use and not for telecom and WE were licensed vice versa. As far as retail sales of the tubes were concerned it made no difference, but a manufacturer who bought WE tubes and put them in a consumer radio or product would have been a license violator. Brook, if memory serves, got 'round this by making an amp that could use either 2A3 or 300B tubes with a little rewiring. It came with 2A3s and could be easily retrofitted. There were many homebrews-all push pull, however-with 300B tubes in the late forties and early fifties. The real triode crazies preferred other tubes, even before the mentally disturbed Bob Fulton came on the scene. |
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#32
Posted to rec.audio.tubes
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Brook 10C's
Another thing, only a small percentage of Brooks sold used the
sliding bias circuit. Most preferred those without it. Lincoln Walsh did a stupendous manufacturing job, going through a lot of winding experiments with those ordinary LOOKING transformers. Even Peerless-the real Peerless-couldn't match them. But they did look pretty plain, because they were assumed to be going in a cabinet of some type in those days. Yes, I have heard the Brook amplifiers, and yes, they really are all that and a bag of chips, within their designed operating range. Brook went tits up because of low sales, because of plebian appearance and lack of specsmanship, and also because Lincoln Walsh was apparently quite troubled, although I don't know in what manner. He was an old man when he did the Brook amps, and eventually went on to invent the Ohm speaker driver, dying before the first one was sold. He was really a PIONEER of hi-fi, building serious amps and speakers before WWII. If someone were able to duplicate the transformers, particularly the driver chokes (the ALtec 1570B uses an extension of this idea) it would be a fine DIY project. I suspect the thing that phagott Kevin Deal-he sounds queerer on the phone than Magnequeef Mike-is selling as the "Adaptive Auto Bias" is more or less a solid state update of the Brook idea. |
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#33
Posted to rec.audio.tubes
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Brook 10C's
"flipper" wrote in message ... On Wed, 19 Oct 2011 01:02:54 -0700 (PDT), Patrick Turner wrote: snip Unfortunately my tube models are not accurate at very low plate voltages (something I've run into before) but adjusting things to meet his criteria I have successfully modeled the 6SN7 'detector' so that it holds plate voltage within .4V of 80mA idle with peak currents through Rk corresponding to what you call 'Vdc' equivalent to a 190mA average. If, however, I put a 190mA idle, creating an *actual DC* "Vdc" of 2.87V (vs the 1.2V 80mA idle) plate shifts 8.8V, which is close to 20 times the shift when it's 'AC'. I also managed to model it using a 6DJ8. In short, it works if you properly bias the tube Correct! The 6SN7 trough detector is not just a common grid amplifier stage as Partick is trying (in vain) to convince us. It is a detector close to cutoff. For example, if the quiescent current through 15R is meant to be 80mA, then the cathode of 6SN7 would be at Vk=+1.2V. To keep the trough detector close to cut-off, its plate voltage should be about Vk * mu. For 6SN7 mu=20, so plate voltage should be around 24V or even less (given thermal emission potential and the fact that mu is smaller at low currents). Plate current would be small, probably 50...150uA. High gm sharp cut-off tubes like 6DJ8 will make a better trough detector, but a transistor would be even better. Could be a n-JFET -- just select a specimen (e.g., BFT46) with 1.2V cutoff voltage (or adjust 15R). |
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#34
Posted to rec.audio.tubes
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Brook 10C's
On Oct 21, 6:28*pm, flipper wrote:
On Thu, 20 Oct 2011 21:36:47 -0700 (PDT), Patrick Turner wrote: On Oct 21, 2:53*pm, flipper wrote: On Wed, 19 Oct 2011 01:02:54 -0700 (PDT), Patrick Turner wrote: snip And while we are on the subject of Brook 10C, Our Dear Flipper maintains that there is no Vdc change across the 15r common Rk for a pair of 2A3, when they have to power a low RLa-a to make 30W with a continuous sine wave. I never said any such thing. Not exactly, but indirectly, because you seem to be insisting that a change in Vdc at the DC amp output remains unchanged because of that stuff about time constants, and trough detection going on, and the Vac across the 15r, You wrongly insisting that if plate voltage is constant then Ek 'must be constant' is YOUR 'conclusion' and it's disingenuous to then claim *I* said it. But my knowledge tells me Your knowledge doesn't include constructing a Walsh Automatic Bias Control. Nor does your knowledge. You have not built the Brook 10C bias control circuit, so you don't know what you are talking about. So there is no need for me to reply to you. You are a really dumb stupid **** for thinking you are right when you do not have any evidence to support your opinion, except your interpretation of the Walsh patent. If you are to have any credibility, you MUST BUILD AND MEASURE THE Brook 10C, although it can be any existing PP amp with fixed bias; you don't need to have 2A3, trioded 6L6 will do. When you have posted several pages on the subject, and done the work, only then can anyone with a brain suspect you might really know what ya talkin about. To achieve credidility you have to adhere to basic scientic methods. So stop prattling on like a stupid child about what ya dunno about. Patrick Turner. |
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#35
Posted to rec.audio.tubes
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Brook 10C's
Dear readers of r.a.t, below we have the MOST PREVALENT EXAMPLE OF A STUPID IDIOT, i.e, one Mr Flipper, who dare not use his real name, and he thinks he so right about something he has not constructed or observed, tested, and graphed, and he insists that every word in a patent is the whole truth and nothing but the truth, rather like someone who believes in the absolute truth of the Bible. Its pointless to discuss anything with Flipper because he just cannot accept that his **** stinks. I know mine does, He always thinks he's right, and that his opinion is the only one worth considering, but this makes him an ARROGANT ****, someone to always despise, and someone to always mistrust. No need for me to reply to the crap below, because Flipper continues to give ZERO information based on facts to support his opinions about the Brook 10C amp. Patrick Turner. On Oct 21, 6:51*pm, flipper wrote: On Thu, 20 Oct 2011 21:54:00 -0700 (PDT), Patrick Turner wrote: I still don't think you understand this Brook circuit you are trying to discuss, and only by building it and testing is will you get it, IMHO. So build one so you can understand it. I've read the rest of your reply, but see no point in continuing to argue. Wise choice since I have a filed and approved patent plus a manufactured and sold device based on the same principle to back up my position. That you take the word of somebody or anybody who patented an ampifier gimick shows you lack the ability to have doubts, and to ever think that you could ever be wrong. Utter nonsense. As proof one has only to see how I 'doubt' you. I do not, however, just presume everyone else are liars, as you've done with the Walsh patent. All things claimed by a train full of people still need validation on your workbench. *Words in patents and your modelling are NOT reality. It's a hell of a lot closer than you simply ****ing about it. Many ppl can be wrong about an idea, even though it seems so right. When Challenger fell from the sky, had not a huge certainty been established about the integrity of the Shuttle? But the fukkin thing still went wrong, and engineers had to re-assess. Irrelevant babble. So when you jump up an down in triumph because you have concluded I'm wrong, the world will just think your'e a dumb jerk. I conclude you can't, or won't, read because I see what you quote and how you 'interpret' plain English to say something other than what it plainly says. And then, given the choice between a patent and a manufactured product vs your 'opinion', I concluded you're wrong because you refuse to even properly read how the circuit is intended to work. And I'd come to the exact same conclusion with an auto mechanic who couldn't grasp a fuel injection patent because the odds of him being 'right' about whether it works or not, when he can't even get the description down right, would be nothing but a wild stroke of luck. You have to work a lot harder at proving you are right. I've got so much paid work I don't have time to build Brook's idea, so I don't much care if I lose this argument. I don't like Brook's idea. "Not invented here" syndrome. Having a cascaded 6SN7 to control bias could lead to smoke; if the tube ever fails, or the negative supply fails, watch out. Failure modes are an entirely different matter but you have a point with failure of the second DC amp. As for failure of the negative rail, any fixed bias amp will go insane if grid bias is lost; I can't think of very many ppl who have included Vdc amps in their tube amp schematics; most bean counters always said no anyway. Your favorite mythical boogie man, the 'bean counter'. You've never met one and never designed anything in a company environment but, by golly, that doesn't stop your fantasies. Patrick Turner.- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - |
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#36
Posted to rec.audio.tubes
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Brook 10C's
You're quite the pratter yourself, Patrick. You've got a very prominent
problem with the Bible. I read this newsgroup to glean information and your ****ing on the Bible is getting tiresome. It has nothing to do with the topic at hand or the topic of this newsgroup. Get ****ed with something else. Eddie "Patrick Turner" wrote in message ... Dear readers of r.a.t, below we have the MOST PREVALENT EXAMPLE OF A STUPID IDIOT, i.e, one Mr Flipper, who dare not use his real name, and he thinks he so right about something he has not constructed or observed, tested, and graphed, and he insists that every word in a patent is the whole truth and nothing but the truth, rather like someone who believes in the absolute truth of the Bible. Its pointless to discuss anything with Flipper because he just cannot accept that his **** stinks. I know mine does, He always thinks he's right, and that his opinion is the only one worth considering, but this makes him an ARROGANT ****, someone to always despise, and someone to always mistrust. No need for me to reply to the crap below, because Flipper continues to give ZERO information based on facts to support his opinions about the Brook 10C amp. Patrick Turner. On Oct 21, 6:51 pm, flipper wrote: On Thu, 20 Oct 2011 21:54:00 -0700 (PDT), Patrick Turner wrote: I still don't think you understand this Brook circuit you are trying to discuss, and only by building it and testing is will you get it, IMHO. So build one so you can understand it. I've read the rest of your reply, but see no point in continuing to argue. Wise choice since I have a filed and approved patent plus a manufactured and sold device based on the same principle to back up my position. That you take the word of somebody or anybody who patented an ampifier gimick shows you lack the ability to have doubts, and to ever think that you could ever be wrong. Utter nonsense. As proof one has only to see how I 'doubt' you. I do not, however, just presume everyone else are liars, as you've done with the Walsh patent. All things claimed by a train full of people still need validation on your workbench. Words in patents and your modelling are NOT reality. It's a hell of a lot closer than you simply ****ing about it. Many ppl can be wrong about an idea, even though it seems so right. When Challenger fell from the sky, had not a huge certainty been established about the integrity of the Shuttle? But the fukkin thing still went wrong, and engineers had to re-assess. Irrelevant babble. So when you jump up an down in triumph because you have concluded I'm wrong, the world will just think your'e a dumb jerk. I conclude you can't, or won't, read because I see what you quote and how you 'interpret' plain English to say something other than what it plainly says. And then, given the choice between a patent and a manufactured product vs your 'opinion', I concluded you're wrong because you refuse to even properly read how the circuit is intended to work. And I'd come to the exact same conclusion with an auto mechanic who couldn't grasp a fuel injection patent because the odds of him being 'right' about whether it works or not, when he can't even get the description down right, would be nothing but a wild stroke of luck. You have to work a lot harder at proving you are right. I've got so much paid work I don't have time to build Brook's idea, so I don't much care if I lose this argument. I don't like Brook's idea. "Not invented here" syndrome. Having a cascaded 6SN7 to control bias could lead to smoke; if the tube ever fails, or the negative supply fails, watch out. Failure modes are an entirely different matter but you have a point with failure of the second DC amp. As for failure of the negative rail, any fixed bias amp will go insane if grid bias is lost; I can't think of very many ppl who have included Vdc amps in their tube amp schematics; most bean counters always said no anyway. Your favorite mythical boogie man, the 'bean counter'. You've never met one and never designed anything in a company environment but, by golly, that doesn't stop your fantasies. Patrick Turner.- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - |
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#37
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Are you the same Ed Morris that once worked for R&S?
Cheers, John |
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#38
Posted to rec.audio.tubes
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Brook 10C's
On Oct 25, 2:46*am, "Edward Morris" wrote:
You're quite the pratter yourself, Patrick. *You've got a very prominent problem with the Bible. *I read this newsgroup to glean information and your ****ing on the Bible is getting tiresome. *It has nothing to do with the topic at hand or the topic of this newsgroup. *Get ****ed with something else. Eddie I guess the word pratter must be american slang for arogant **** or dick head or something else negative, and I don't mind what you call me, because that won't stop those wanting to know the truth about a Brook 10C. Then you've mentioned I have a problem with the Bible, and I'm assuming you mean the Old Testament, and presumably the New Testament written many years after Christ's death. There is much wisdom in such old books which tell us how to get to Heaven, but as someone very famous said in about 1500, the Bible does not tell us how the heavens go, and I recall Rome was vastly browned off by this upstart no-good arsole and the church treated him very poorly. Trouble was, the bloke was right, and Rome was wrong, about the Earth going around the Sun, rather than agreeing with Rome's idea the Sun went around the Earth. Turns out that space is so infinitely large, that anyone's ideas about who or what God is MUST be all bull****, because infinite info about infinite sized universes and infinite details can't fit into little dumb Homo Sapien brains which are only marginally brighter than a monkey's, from which they evolved rather slowly. Then there are all these stories about God the Father, God the Son, and God the Holy Ghost, and the story of the Virgin Mary, who got pregnant with Christ without anyone sticking a dick up her. Just where does one begin to make a list of Bull**** Items in the Bible? All too difficult for me to find the time, and instead I concentrate on being a useful solderer making connections to favour music, and to serve up a bitta heaven right here on Earth, and I figure I don't have to be a God Botherer while I'm serving Humanity, and Hu-womanity, should they need a fix for a problem, whatever. Perhaps by "Bible" you mean RDH4, in which case there is nothing about getting to heaven, but everything about how the heavens go, ie, stories about the workings of physics in relation to vacuum tubes, and thingemejigs with L, C and R within. So I don't have too much to disagree with in RDH4; it leaves out any mention of God, thank Goodness. For many people, the Old Testamant is the only one True Book, and everything which was before or after it is basically bull**** not worth reading. That's OK, I don't mind, but I'll still remain me, ever questioning all I see and hear, and open to absorbing good info wherever I find it, and its years since I studied the Bible, and if I did, I doubt I'd be a better person, but probably would be a mal- contented person because such grand old books cannot tell me what I like to consider in the universe, without myths and fantasies. So what have you got to say about the Brook 10C? Last time I posted I was just fed up with ppl NOT supporting their claims about the bias control circuit in the Brook 10C, but they were so sure they were correct. Patrick Turner. |
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#39
Posted to rec.audio.tubes
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Brook 10C's
On Nov 2, 10:07*pm, Patrick Turner wrote:
On Oct 25, 2:46*am, "Edward Morris" wrote: You're quite the pratter yourself, Patrick. *You've got a very prominent problem with the Bible. *I read this newsgroup to glean information and your ****ing on the Bible is getting tiresome. *It has nothing to do with the topic at hand or the topic of this newsgroup. *Get ****ed with something else. Eddie I guess the word pratter must be american slang for arogant **** or dick head or something else negative, and I don't mind what you call me, because that won't stop those wanting to know the truth about a Brook 10C. Then you've mentioned I have a problem with the Bible, and I'm assuming you mean the Old Testament, and presumably the New Testament written many years after Christ's death. There is much wisdom in such old books which tell us how to get to Heaven, but as someone very famous said in about 1500, the Bible does not tell us how the heavens go, and I recall Rome was vastly browned off by this upstart no-good arsole and the church treated him very poorly. Trouble was, the bloke was right, and Rome was wrong, about the Earth going around the Sun, rather than agreeing with Rome's idea the Sun went around the Earth. Turns out that space is so infinitely large, that anyone's ideas about who or what God is MUST be all bull****, because infinite info about infinite sized universes and infinite details can't fit into little dumb Homo Sapien brains which are only marginally brighter than a monkey's, from which they evolved rather slowly. Then there are all these stories about God the Father, God the Son, and God the Holy Ghost, and the story of the Virgin Mary, who got pregnant with Christ without anyone sticking a dick up her. Just where does one begin to make a list of Bull**** Items in the Bible? All too difficult for me to find the time, and instead I concentrate on being a useful solderer making connections to favour music, and to serve up a bitta heaven right here on Earth, and I figure I don't have to be a God Botherer while I'm serving Humanity, and Hu-womanity, should they need a fix for a problem, whatever. Perhaps by "Bible" you mean RDH4, in which case there is nothing about getting to heaven, but everything about how the heavens go, ie, stories about the workings of physics in relation to vacuum tubes, and thingemejigs with L, C and R within. So I don't have too much to disagree with in RDH4; it leaves out any mention of God, thank Goodness. For many people, the Old Testamant is the only one True Book, and everything which was before or after it is basically bull**** not worth reading. That's OK, I don't mind, but I'll still remain me, ever questioning all I see and hear, and open to absorbing good info wherever I find it, and its years since I studied the Bible, and if I did, I doubt I'd be a better person, but probably would be a mal- contented person because such grand old books cannot tell me what I like to consider in the universe, without myths and fantasies. So what have you got to say about the Brook 10C? Last time I posted I was just fed up with ppl NOT supporting their claims about the bias control circuit in the Brook 10C, but they were so sure they were correct. Patrick Turner. Mr Morris has replied to me in private with subject matter that is entirely off the topic of the Brook 10C, ie, he has rambled on and on and that's OK, but he has not done anything positive to determine whether or not the Brook 10C bias control is any good or not. I present his private email here because he should have addressed the group, not just me. """You like to ramble don't you Patrick? You type and type and ramble about things you're guessing about. I have nothing to say about the Brook 10C. You are the one who rambled about the Bible in the Brook 10C thread. I didn't. Edward Morris"""" ----- Original Message ----- From: "Patrick Turner" Newsgroups: rec.audio.tubes Sent: Wednesday, November 02, 2011 6:07 AM Subject: Brook 10C's On Oct 25, 2:46 am, "Edward Morris" wrote: You're quite the pratter yourself, Patrick. You've got a very prominent problem with the Bible. I read this newsgroup to glean information and your ****ing on the Bible is getting tiresome. It has nothing to do with the topic at hand or the topic of this newsgroup. Get ****ed with something else. And BTW, he has nothing to say which would change my doubt about what's been scribbled in the Bible, apparently by those with vivid imaginations, or by those who like to get control over other people by writing a book at a time when there were SFA books around to read, so then then it was easy to enforce biblical propaganda and enforce laws and order, such as the 10 commandments. Such books and rules led to monastories or ruling elite who could con others into doing all sorts of BS things such as building the Pyramids, or the Vatican, while sweating from work and being poorly paid while fat guys in fancy dress paraded around prosletizing Bible content, and maybe ****ing little boys or nuns on their rounds. The 10 commandments are not a bad set of rules. Usually most societies eventually end up inventing such laws, give or take a few, and then invent beheading and burnings at stakes to enforce dogma. Some move forward to having serious religious wars and conducting Crusades. Eventually, societies get rich and then just **** on dogma and most commandments yet life proceeds remarkably well. Rules are made to be broken, hence the occasional Depression, and a woeful divorce rate, and 20,000 shootings in the USA, land of the Free, and goodness knows how many traffic fatalities. ( Could the Amish really have the answers? ) But before that, Sometimes things fell apart of course, and there was a Plague anyway, despite ppl praying to God about it. They'd kill cats in cities because they thought them to be evil witches and then that allowed more rats and their fleas, so hence the Plagues. That meant that 1/2 the poplulation would inherit a windfall in the form of the inheritance from those who died. So Plagues were not all bad for everyone if you survived. But a better solution was scientific thought which led to the knowledge about city hygiene, good plumbing and sewers, and inventing so very much to avoid **** happening without praying to God or reading the Bible at all. If there was a bit more scientific thought from Flipper et all, we'd see more tolerance of variablity in opinions, and we'd also see the TRUTH about the brook 10C which so far niether myself or anyone else has established beyond all reasonable doubt. Patrick Turner. |
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#40
Posted to rec.audio.tubes
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Brook 10C's
Mr. Turner you can't be that daft? I could give a flip about the Brook 10C.
I don't own one nor do I care to own one. Try to understand this, ok?? In a number of messages you send to this group, you put down the Bible, even thought it has nothing to do with the topic of the message. I believe in the Bible but you don't see me here message after message with my pro-Bible stance. You have your biases against the Bible but I don't understand why you continue to interject your biases in messages that have nothing to do with the Bible???? Keep you biases to yourself. Edward Morris "Patrick Turner" wrote in message ... On Nov 2, 10:07 pm, Patrick Turner wrote: On Oct 25, 2:46 am, "Edward Morris" wrote: You're quite the pratter yourself, Patrick. You've got a very prominent problem with the Bible. I read this newsgroup to glean information and your ****ing on the Bible is getting tiresome. It has nothing to do with the topic at hand or the topic of this newsgroup. Get ****ed with something else. Eddie I guess the word pratter must be american slang for arogant **** or dick head or something else negative, and I don't mind what you call me, because that won't stop those wanting to know the truth about a Brook 10C. Then you've mentioned I have a problem with the Bible, and I'm assuming you mean the Old Testament, and presumably the New Testament written many years after Christ's death. There is much wisdom in such old books which tell us how to get to Heaven, but as someone very famous said in about 1500, the Bible does not tell us how the heavens go, and I recall Rome was vastly browned off by this upstart no-good arsole and the church treated him very poorly. Trouble was, the bloke was right, and Rome was wrong, about the Earth going around the Sun, rather than agreeing with Rome's idea the Sun went around the Earth. Turns out that space is so infinitely large, that anyone's ideas about who or what God is MUST be all bull****, because infinite info about infinite sized universes and infinite details can't fit into little dumb Homo Sapien brains which are only marginally brighter than a monkey's, from which they evolved rather slowly. Then there are all these stories about God the Father, God the Son, and God the Holy Ghost, and the story of the Virgin Mary, who got pregnant with Christ without anyone sticking a dick up her. Just where does one begin to make a list of Bull**** Items in the Bible? All too difficult for me to find the time, and instead I concentrate on being a useful solderer making connections to favour music, and to serve up a bitta heaven right here on Earth, and I figure I don't have to be a God Botherer while I'm serving Humanity, and Hu-womanity, should they need a fix for a problem, whatever. Perhaps by "Bible" you mean RDH4, in which case there is nothing about getting to heaven, but everything about how the heavens go, ie, stories about the workings of physics in relation to vacuum tubes, and thingemejigs with L, C and R within. So I don't have too much to disagree with in RDH4; it leaves out any mention of God, thank Goodness. For many people, the Old Testamant is the only one True Book, and everything which was before or after it is basically bull**** not worth reading. That's OK, I don't mind, but I'll still remain me, ever questioning all I see and hear, and open to absorbing good info wherever I find it, and its years since I studied the Bible, and if I did, I doubt I'd be a better person, but probably would be a mal- contented person because such grand old books cannot tell me what I like to consider in the universe, without myths and fantasies. So what have you got to say about the Brook 10C? Last time I posted I was just fed up with ppl NOT supporting their claims about the bias control circuit in the Brook 10C, but they were so sure they were correct. Patrick Turner. Mr Morris has replied to me in private with subject matter that is entirely off the topic of the Brook 10C, ie, he has rambled on and on and that's OK, but he has not done anything positive to determine whether or not the Brook 10C bias control is any good or not. I present his private email here because he should have addressed the group, not just me. """You like to ramble don't you Patrick? You type and type and ramble about things you're guessing about. I have nothing to say about the Brook 10C. You are the one who rambled about the Bible in the Brook 10C thread. I didn't. Edward Morris"""" ----- Original Message ----- From: "Patrick Turner" Newsgroups: rec.audio.tubes Sent: Wednesday, November 02, 2011 6:07 AM Subject: Brook 10C's On Oct 25, 2:46 am, "Edward Morris" wrote: You're quite the pratter yourself, Patrick. You've got a very prominent problem with the Bible. I read this newsgroup to glean information and your ****ing on the Bible is getting tiresome. It has nothing to do with the topic at hand or the topic of this newsgroup. Get ****ed with something else. And BTW, he has nothing to say which would change my doubt about what's been scribbled in the Bible, apparently by those with vivid imaginations, or by those who like to get control over other people by writing a book at a time when there were SFA books around to read, so then then it was easy to enforce biblical propaganda and enforce laws and order, such as the 10 commandments. Such books and rules led to monastories or ruling elite who could con others into doing all sorts of BS things such as building the Pyramids, or the Vatican, while sweating from work and being poorly paid while fat guys in fancy dress paraded around prosletizing Bible content, and maybe ****ing little boys or nuns on their rounds. The 10 commandments are not a bad set of rules. Usually most societies eventually end up inventing such laws, give or take a few, and then invent beheading and burnings at stakes to enforce dogma. Some move forward to having serious religious wars and conducting Crusades. Eventually, societies get rich and then just **** on dogma and most commandments yet life proceeds remarkably well. Rules are made to be broken, hence the occasional Depression, and a woeful divorce rate, and 20,000 shootings in the USA, land of the Free, and goodness knows how many traffic fatalities. ( Could the Amish really have the answers? ) But before that, Sometimes things fell apart of course, and there was a Plague anyway, despite ppl praying to God about it. They'd kill cats in cities because they thought them to be evil witches and then that allowed more rats and their fleas, so hence the Plagues. That meant that 1/2 the poplulation would inherit a windfall in the form of the inheritance from those who died. So Plagues were not all bad for everyone if you survived. But a better solution was scientific thought which led to the knowledge about city hygiene, good plumbing and sewers, and inventing so very much to avoid **** happening without praying to God or reading the Bible at all. If there was a bit more scientific thought from Flipper et all, we'd see more tolerance of variablity in opinions, and we'd also see the TRUTH about the brook 10C which so far niether myself or anyone else has established beyond all reasonable doubt. Patrick Turner. |
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