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Patrick Turner Patrick Turner is offline
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Default KT90EH review and relability.

Some might wonder about the reliability of Russian made output tubes,
notably the KT90EH sold by New Sensor in New York.
I have a positive story to tell.
In 1996, I built an 8585 amp shown at http://www.turneraudio.com.au/8585-a...ober-2006.html
The initial tubes I used were new GE6550A which were regarded as the
best 6550 available.
I sold the amp in about 2003, and by 2004, some GE 6550 had
considerable reverse grid current, and showed signs of wear. The owner
had me upgrade the circuit to that shown at the link above after a
routine service, and with the EL84 drivers the Rg to each 6550 was
reduced to 100k, and this limited reverse grid current at idle, and
helped keep the bias voltage stable. 6550EH were also fitted to
replace the aged GE6550. The owner was very happy with the mod, but
had the desire to try other tubes and the 6550EH were replaced with
KT90EH. In about 2005, the amp was sold to its present owner who
drives 3 stacked pairs of fully re-engineered Quad ESL57. He's been
delighted with the sound, and has used the system every day since
2005. John Hall of Melbourne had re-engineered the ESL.

Now last week, the amp stopped working, and was sent to me for a fix,
its first breakdown since 1996. It turned out all four 5 Watt "75V"
zener diodes to shunt regulate the screen voltage had all changed
their zener voltage to lower voltages and so Eg = +220V instead of a
normal +330V, thus turning off anode current to all OP tubes, and no
collateral damage occurred. I've replaced the zeners with a far better
shunt reg based in a pair of series BU208P + MJE340 darlington
connected bjts on a heatsink because it seems that particular brand of
5W zeners is subject to failure after passing years. In fact the 75V
zeners had a zener voltage of around 82V when new. Their working
condition was with about 20mA in each, and 82V, and that's 1.64Watts,
and I'd cramped them between plate of aluminium and the aluminium
chassis with lots of heat paste to keep 'em cool as cucumbers.
Didn't stop them frying it seems.

The condition of the 8 x KT90EH was the same as if I had plugged in a
set of new tubes, but these have been used a lot since 2005, about 6
years, at least each day says the owner, who was surprised the amp
didn't need new tubes, and that it needed such little work.

The KT90 conditions are :- fixed bias, Ea = +475V,
Ia = 32mA, Eg2 = +330V, Ig2 = 2mA, and Eg1 = -37V.
The differences between applied Eg1 and Ia were less than 5%, and
between Ig2, less than 10%, and the Vdc across each 8 x 100k Rg less
than 0.03V, with little noise, ie, the tubes measured just like a new
set. I think they are lasting better than GE6550A.

The EL84EH in triode are also showing zero signs of wear. All other
NOS Australian made input tubes are also working as new.

Manwhile, the 6550EH which were replaced by KT90EH were supplied to
other owners at a low cost and appear to be working just fine.

I do hope the Russians are keeping up their good work, and If I could
send a bottle of Vodka, I would.

Patrick Turner.
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Default KT90EH review and relability.

On Oct 15, 3:47*pm, flipper wrote:
On Fri, 14 Oct 2011 19:42:32 -0700 (PDT), Patrick Turner

wrote:

snip

In fact the 75V
zeners had a zener voltage of around 82V when new. Their working
condition was with about 20mA in each, and 82V, and that's 1.64Watts,
and I'd cramped them between plate of aluminium and the aluminium
chassis with lots of heat paste to keep 'em cool as cucumbers.
Didn't stop them frying it seems.


You didn't mention what the part number was but, FYI, if they're the
typical plastic case 5 Watt zener then heatsinking the case doesn't
accomplish much, if anything. The rating depends on dissipation
through the leads soldered to the 'heatsink', which is typically a
'large' PC board trace area but can be something more robust.

The leads 'to the heatsink' should also be as short as possible.


The "75V" zeners are of unknown asian origin, maybe 8mm long x 5mm dia
hard plastic bodies. So when they are cramped between Al plates with
generous heat paste, they still may get warm internally. 1.64W isn't
much though. But at just after amp turn on, and before OP tubes
conduct, the current is 50mAdc, which is 4.1Watts, which one might
think was OK until the screens conducted some current within 15
seconds and Ea dropped to reduce the total Ig2 supply to a steady 42mA
with about 1/2 that in Zeners and 1/2 in KT90 screens. So probably the
repeating heating cycles on the zeners affected their zener voltage.
I've known zeners to be a bit dodgy in this aspect, but as long as one
doesn't exceed 1/3 the Pd rating for continuous use they are OK at
least for the short term. I could have used say 10 x 33V x 5W Zeners,
which may have coped better.
Sometimes I've wrapped a U shaped piece of copper around zeners with a
screw to hold them to a chassis and with silicone or heat paste, and
such allows one to hold a finger to the zener indefinately, ie, T
45C, which should be OK. I have used other smaller sized zeners also
rated for 75V and 5W in other locations with no troubles, ever, but
usuually Idc max is 10mA, for 0.75W Pd max, so hanging them across a
pair of lugs on a tag strip is OK and they run cool.

I'm ammending my 8585 schematics to show the use of bjts to shunt reg
the Eg2 supply. The reason for shunt reg instead of series reg should
be obvious; if you have a wayard tube with excessive Ig2, say 50mA,
the series R of 3k6 between B+ of +480V and the screen shunt reg
develops a voltage of 180Vdc, and of course other tubes still draw
Ig2, so maybe the drop is 252V, so that Eg2 then drops to +228V, and
the amp becomes silent, and action is taken to find out why. Where you
have a series reg, the Ig2 might rise from 20mA to 70mA and the faulty
tube could more likely cause colateral damage as it melts down. Shunt
reg "wastes" some current and Watts in the reg, but it is a slight
amount compared to the hundreds of Watts a big amp uses at idle, even
with low Ia bias currents as I am using.

Patrick Turner.
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Alex Pogossov Alex Pogossov is offline
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Default KT90EH review and relability.


"Patrick Turner" wrote in message
...
.... I've replaced the zeners with a far better
shunt reg based in a pair of series BU208P + MJE340 darlington
connected bjts on a heatsink because it seems that particular brand of
5W zeners is subject to failure after passing years. In fact the 75V
zeners had a zener voltage of around 82V when new. Their working
condition was with about 20mA in each, and 82V, and that's 1.64Watts,
and I'd cramped them between plate of aluminium and the aluminium
chassis with lots of heat paste to keep 'em cool as cucumbers.
Didn't stop them frying it seems.


A Hi-V Zener is a very good regulator, and if your 75V rated zeners had 82V
(!!!!????) drop -- they were faulty from the start.

Secondly, why on Earth do you run them at 20mA? 0.2mA would be quite enough,
but if you are "conservative", run 1mA through them. Of course in this case
they need to be followed by a darlington.

If a darlington is not an option, and the regulator *has to be* really
shunt, and to shunt large currents to ground -- here is a trick.
a) Take a TO-220 PNP uninsulated tab transistor;
b) Connect the string of Zeners between base and collector;
c) Bolt the TO-220 collector tab to the chassis -- good and easy heatsink;
d) Use the emitter lead as the "cathode" of the pseudo-zener. 0.7V will be
added to your regulated voltage

Zener current will reduce beta times. For better regulation connect 470R
between base and emitter -- it will give about 1.5mA stable initial current
through the zeners.

Zeners are very noisy though. It is always good to connect a capacitor
across a zener. For audio probably any electrolytic will do. For radio
applications -- 0.1uF ceramic with short leads close to the zener case.

Regards,
Alex


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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default KT90EH review and relability.


"Patrick Turner"

In about 2005, the amp was sold to its present owner who
drives 3 stacked pairs of fully re-engineered Quad ESL57. He's been
delighted with the sound, and has used the system every day since
2005. John Hall of Melbourne had re-engineered the ESL.



** Triple stacked ESL57s ????

That is SOME kind of speaker array !!!

I am very familiar with twin stacked ESL57 set ups - right pains in the
arse they are too.

But triples ??

All wired in parallel ??

( Massive low Z at HF )

Or maybe spread about in an ersatzes surround regime ??

Enquiring minds need to know...




.... Phil





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Patrick Turner Patrick Turner is offline
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Default KT90EH review and relability.

On Oct 15, 5:20*pm, "Alex Pogossov" wrote:
"Patrick Turner" wrote in message

...

.... I've replaced the zeners with a far better
shunt reg based in a pair of series BU208P + MJE340 darlington
connected bjts on a heatsink because it seems that particular brand of
5W zeners is subject to failure after passing years. In fact the 75V
zeners had a zener voltage of around 82V when new. Their working
condition was with about 20mA in each, and 82V, and that's 1.64Watts,
and I'd cramped them between plate of aluminium and the aluminium
chassis with lots of heat paste to keep 'em cool as cucumbers.
Didn't stop them frying it seems.


A Hi-V Zener is a very good regulator, and if *your 75V rated zeners had 82V
(!!!!????) drop -- they were faulty from the start.


Zeners are a kind of simplest solution, not perfect, but quite good
enough most of the time where the Pd is kept low, but not too low. The
actual zener voltage one measures is sometimes not exactly what the
item is supposed to be, and it varies with current, and zeners do have
a finite Rout. I don't repair many solid state amps, and I employ a
guy who does, and sure enough faulty zeners do occur often enough to
be a bit cautious about using them at all.

Secondly, why on Earth do you run them at 20mA? 0.2mA would be quite enough,
but if you are "conservative", run 1mA through them. Of course in this case
they need to be followed by a darlington.


Its a shunt reg. There is a 3k6 series R, 25W rated from B+ of +480Vdc
to the screens which draw about 21mA at idle when Eg2 = 330Vdc. So
there is about 20mA in the shunt reg devices. At 1dB below clipping,
Ig2 increases considerably, and the shunt reg devices conduct much
less current to 0V, so that the Eg2 stays close to constant, far more
so than if there were no shunt reg present.

0.2mA would not be enough current in the shunt devices.

If a darlington is not an option, and the regulator *has to be* really
shunt, and to shunt large currents to ground -- here is a trick.
a) Take a TO-220 PNP uninsulated tab transistor;
b) Connect the string of Zeners between base and collector;
c) Bolt the TO-220 collector tab to the chassis -- good and easy heatsink;
d) Use the emitter lead as the "cathode" of the pseudo-zener. 0.7V will be
added to your regulated voltage


Yes, I've done similar to what you suggest with NPN bjt, but I wanted
to get away from using a string of highish voltage zeners.

But often you can't just bolt an NPN bjt to a chassis or heatsink
unless its well insulated because the tab on most TO220 bjts is the
collector, which has to be at high Vdc. The PNP idea looks OK.


So instead, I have a 25V zener, 5W, ( and from stocks which I found
were reliable, ) from emitter of bottom darlington NPN pair to 0V,
then collector goes to emitter of top darlington NPN pair, then top
collector goes to bottom of 3k6 feed resistance and screen
connections. There is a 100uF to bypass screens to 0V.
Then I have a totem pole R network from screens to 0V, 39k0, 39k0, and
6k4, with the two R junctions to darlington pair bases. Works quite
well enough for me I found, and there is only 155Vdc across the
collector to emitters for the transistors. MJE340 has the lowest
rating at 300V, and I just don't like having more than half the Vce
rating across any BJTs.

Using your PNP idea, you could have two series PNP devices I guess,
with the bottom one's base to 1/2 way up the zener string, and
appropriate insulations.


Zener current will reduce beta times. For better regulation connect 470R
between base and emitter -- it will give about 1.5mA stable initial current
through the zeners.


Yes, all doable, but I have good enough reg without a long zener
string.



Zeners are very noisy though. It is always good to connect a capacitor
across a zener. For audio probably any electrolytic will do. For radio
applications -- 0.1uF ceramic with short leads close to the zener case.


Yeah, I know about the noise, and I usually always have a large cap to
bypass the target load. Sometimes I put the zeners so there is some R
from them to the bypass cap, not enough R to affect reg much, but
enough to give an effective RC filter after and away from the low Z of
the zeners. Usually I use zeners to help ensure excellent LF stability
in amps.

Patrick Turner.

Regards,
Alex




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On Oct 15, 6:25*pm, flipper wrote:
On Fri, 14 Oct 2011 22:56:03 -0700 (PDT), Patrick Turner





wrote:
On Oct 15, 3:47 pm, flipper wrote:
On Fri, 14 Oct 2011 19:42:32 -0700 (PDT), Patrick Turner


wrote:


snip


In fact the 75V
zeners had a zener voltage of around 82V when new. Their working
condition was with about 20mA in each, and 82V, and that's 1.64Watts,
and I'd cramped them between plate of aluminium and the aluminium
chassis with lots of heat paste to keep 'em cool as cucumbers.
Didn't stop them frying it seems.


You didn't mention what the part number was but, FYI, if they're the
typical plastic case 5 Watt zener then heatsinking the case doesn't
accomplish much, if anything. The rating depends on dissipation
through the leads soldered to the 'heatsink', which is typically a
'large' PC board trace area but can be something more robust.


The leads 'to the heatsink' should also be as short as possible.


The "75V" zeners are of unknown asian origin, maybe 8mm long x 5mm dia
hard plastic bodies.


Sounds like the 1N53xx series. Those are about 8.5mm by 3.5mm.

So when they are cramped between Al plates with
generous heat paste, they still may get warm internally.


Not just 'warm' inside, 'hot'. The body is not a thermal interface for
them.

1.64W isn't
much though. But at just after amp turn on, and before OP tubes
conduct, the current is 50mAdc, which is 4.1Watts, which one might
think was OK


I don't know. They don't give a free air transient thermal response
but there's hardly any thermal mass there to heat up, meaning I'd
imagine they get damn hot damn fast.

until the screens conducted some current within 15
seconds and Ea dropped to reduce the total Ig2 supply to a steady 42mA
with about 1/2 that in Zeners and 1/2 in KT90 screens. So probably the
repeating heating cycles on the zeners affected their zener voltage.
I've known zeners to be a bit dodgy in this aspect, but as long as one
doesn't exceed 1/3 the Pd rating for continuous use they are OK at
least for the short term. I could have used say 10 x 33V x 5W Zeners,
which may have coped better.
Sometimes I've wrapped a U shaped piece of copper around zeners with a
screw to hold them to a chassis and with silicone or heat paste, and
such allows one to hold a finger to the zener indefinately, ie, T
45C, which should be OK.


That's what I'm trying to tell you. The 'body' surface being a
'comfortable' 45C doesn't mean anything because they are not
heatsinked through the body.

You can't really calculate anything without knowing the 'heatsink' to
ambient thermal resistance because everything is based on lead
temperature, which one derives from the power dissipation and
'heatsink' thermal coefficient to free air, and lead length, which
gives the internal diode to heatsink thermal coefficient.

I.E. The 5 Watt rating is with 3/8 inch leads at 75C (heatsink temp).

There is no 'free air' or '25C' rating. However, one could calculate a
heatsink rating at 50C ambient (not an uncommon rating, although maybe
too low for a tube amp), which would allows a 25C rise on the heatsink
while dissipating 5 Watt. That would mean a 5C/W heatsink soldered to
the leads no longer than 3.8"

Heatsink effectiveness would depend on convection or forced air
cooling. For example, assuming copper traces were 'perfect', the
convection thermal resistance of free air is around 166C/W per square
inch (conservatively high) so to get to 5C/W you'd need 33 square
inches, which isn't chicken feed. On the other hand, it's likely (with
solid state) one end is soldered to a ground plane that acts as a
heatsink.

You can pretty much bet that anyone using the 'full' 5 Watt rating is
employing forced air cooling.

Ironically enough, all that 'heat' in tube amps can be an advantage as
I'm sure you generally put convection cooling holes around your power
tubes. That means the internal air isn't 'still' but is moving due to
the convection currents created by the power tubes. However, if those
aluminum plates blocked the convective airflow they could have caused
more heat retention than what little they could squeeze through a
plastic body that is essentially a thermal blanket around the zener.

Anyway, the point is it isn't trivial.


Indeed, nothing is trivial. All things must be carefully considered
when building tube amps, and sure, I have lots of holes around each
KT90 in the chassis and a bottom chassis cover with 70% open
perforated sheet steel, so air flow is pretty good.
The new arrangement without a zener string should work better, IMHO.
I've nearly completed the much tidied up 8585 PSU schematic, may
upload it later today.

Patrick Turner.
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On Oct 15, 10:30*pm, "Phil Allison" wrote:
"Patrick Turner"



In about 2005, the amp was sold to its present owner who
drives 3 stacked pairs of fully re-engineered Quad ESL57. He's been
delighted with the sound, and has used the system every day since
2005. John Hall of Melbourne had re-engineered the ESL.


** Triple stacked ESL57s * ????

That is SOME kind of speaker array *!!!


Believe me Phil, triple stacked ESL57 is what the man has! I've seen
the pictures.

The speakers were all restored by expert John Hall. The owner also has
an additional pair of ESL57 which he uses with a pair of re-engineered
Quad-II amps.

if you divide the Z of a pair of ESL57 by 3 at all F, you have
speakers which have maybe 10 ohms max Z at bass, then 2.7 ohms at
about 1kHz, and about 0.6 ohms at 18kHz.

The 8585 with KT90 makes what is really a 100100 amp, ie, 100W per
channel, and its OPT ratio is set to suit low Z of the parallel ESL57,
ie, 4.17k : 5 ohms. I've put 3 sets of terminals on the amp for each
channle, and there is 0.6 ohms added from main outlet to to each
speaker connection, so each ESL57 is driven by about 0.8 ohms, and not
the low Rout of the amp. At 1kHz, the amp sees 0.2 ohms plus 2.7 ohms
= 2.9 ohms, and the tubes see 2.42k, and so each pair of KT90 is
loaded by 4.8k at 1khz and they perform effortlessly.
I have the equivalent of at least 4 x Quad-II amps in parallel driving
the stacked speakers. The declining Z of the ESL at HF does not matter
( as Peter Walker knew, ) because audio energy rolls off at F above
1kHz.


I am very familiar with twin stacked ESL57 set ups *- * right pains in the
arse they are too.


Just why would this be? My client had a sturdy timber mounting frame
made and has his speakers speakers arranged to give a nice big panel
which effectively reduces the LF pole because of increased panel area.
I'm not sure how he's lined up the axis, because its possible to
arrange the ESL so they partly function as line array speakers, and
ideally the HF path length should remain constant, so the speakers
should be "concave", and made to suit where one sits. But my client
tells me the sound is utterly awesome, not just able to go loud, but
to go real, and detailed. I doubt he uses higher level than when using
his single pair of ESL57, so the 8585 has not actually got to make
more PO than the two mono Quad-II amps, so my 8585 does not have to
struggle at all. It has it easy.


But triples ??

All wired in parallel *??

( Massive low Z at HF )

Or maybe spread about in an ersatzes surround regime ??

Enquiring minds need to know...

... *Phil


The system is a plain stereo system, speakers apart and out from room
corners, room maybe 200cu.metres. I have not visited the client's
mansion.

One could have all ESL speakers in series, but then the Z goes high,
but to do that right, one should have a speaker matching tranny so the
amp sees say 8 ohms at 1kHz, then the Sec has a 24 ohm winding with 2
taps at 1/3 and 2/3 along the winding. It is a custom job to wind such
a matching tranny.

To get a better load match from any amp to some supposedly difficult
load, ie, one that has a horribly low Z somewhere, one might buy a
ready made toroidal matching tranny from www.zeroimpedance.com
I've seen two clients of mine try these and both said they liked
results. Bleedin' expensive though. I measured a pair and they had BW
over 1Mhz and negligible core sat or resistance losses. They were
wound very un-tidily, but they worked OK.

Old ancient POS speakers such as AR9, with 1.3 ohms Z at around 100Hz
are far more difficult to drive than most ESLs because Z is low in the
band where a lot of power has to occur. AR bass speaker drivers at
that time, late 1970s, were truly godamn awful, Z = 3.6 ohms, and
sensitivity extremely low, so AR was forced to wire 2 in parallel, and
the LC crossover added to the woes. Such speakers killed many an SS
amp. Thermal expiry. A matching tranny with such speakers is mandatory
IMHO, and it allows use of a 50W amp and one does not then need to buy
a Krell or other POS to cope with low Z loading.

Patrick Turner.





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"Patrick Turner

"Phil Allison"


** Triple stacked ESL57s ????

That is SOME kind of speaker array !!!


Believe me Phil, triple stacked ESL57 is what the man has! I've seen
the pictures.

The speakers were all restored by expert John Hall. The owner also has
an additional pair of ESL57 which he uses with a pair of re-engineered
Quad-II amps.

if you divide the Z of a pair of ESL57 by 3 at all F, you have
speakers which have maybe 10 ohms max Z at bass, then 2.7 ohms at
about 1kHz, and about 0.6 ohms at 18kHz.


** That makes any speaker lead inductance really show up.

Cables need to be kept very short ( like 2 metres) or made up from multiple
woven conductors.

Tocord ( aka Mogami Cable ) is ideal.

A very tightly * twisted pair* of heavy gauge wires will do too.


Just why would this be?

** Alignment is critical and keeping al 6 operating perfectly is a pain.


I'm not sure how he's lined up the axis, because its possible to
arrange the ESL so they partly function as line array speakers, and
ideally the HF path length should remain constant, so the speakers
should be "concave", and made to suit where one sits.

** Correct.


But my client
tells me the sound is utterly awesome, not just able to go loud, but
to go real, and detailed.

** Absolutely correct.

Listening to a well set up, stacked Quad ESL57s ruins you for all other
speakers.


The system is a plain stereo system, speakers apart and out from room
corners, room maybe 200cu.metres.


** Sounds just about ideal - long as the room is quiet and heavily damped
too.

The room my friend set up was that sort volume, with carpet lined walls and
a suspended absorber covering about 40% of the ceiling. Near as dammit to
acoustically dead.

He had a pair of KEF B139s in a large ported box for a sub as well - sited
behind the listening position at about the same distance away as the Quads.

Awesome sound and all done prior to the arrival of CDs.


.... Phil




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On Oct 16, 5:10*pm, "Phil Allison" wrote:
"Patrick Turner



"Phil Allison"


** Triple stacked ESL57s ????


That is SOME kind of speaker array !!!


Believe me Phil, triple stacked ESL57 is what the man has! I've seen
the pictures.

The speakers were all restored by expert John Hall. The owner also has
an additional pair of ESL57 which he uses with a pair of re-engineered
Quad-II amps.

if you divide the Z of a pair of ESL57 by 3 at all F, you have
speakers which have maybe 10 ohms max Z at bass, then 2.7 ohms at
about 1kHz, and about 0.6 ohms at 18kHz.

** That makes any speaker lead inductance really show up.

Cables need to be kept very short ( like 2 metres) or made up from multiple
woven conductors.


Yes, as you have a L&R LPF.

Tocord ( aka Mogami Cable ) is ideal.

A very tightly * twisted pair* *of heavy gauge wires will do too.


My client asked me for 3 pairs of L&R speaker cables, 5M long. Each
ESL has its own cable back to the amp. I didn't think about the LR
effect when I made up the cables I suggested which were :- 2 x 5.3M
cat5 cables, with all 8 solid strands of each Cat5 soldered together
into a 4mm banana plug. Then by starting in the centre of each speaker
cable, the two Cat 5 are carefully twisted by folding over each other
and releasing the resulting twisting in free ends each time a few
folds are put in. The result is neater than trying to just winding up
both Cat5 ends of a lead in an electric drill; that's the audio
butcher method. My way takes far longer, but both wires are more
"relaxed" in situ, and twist is nice and even. I figure the L would be
low, and the skin effect minimal, along with rise in RF resistance
because what one has, in effect is thick 8 strand Lotz wire.
Shrinkwrap is used at ends of cables to keep it tidy and identify +/-
with red-black, and different color overall shrink at ends to identify
which speaker cable is which. My client is delighted with the cable
recipe.


Just why would this be?

** Alignment is critical and keeping al 6 operating perfectly is a pain.


Maybe, but my client has had no troubles in many years after John Hall
did the tricks on the old speakers.

He says adjusting balance is critical, and the amp has a balance
control, to give +3db/-6dB gain change for each channel. He uses sig
gene to adjust both channels to give equal outputs. He says that
definately is the best way to get good imaging.." Things suddenly seem
to sweeten up when balance is right" he says, and of course other
family members use the system and accidently knock the balance
control, and oops, there goes the image. I mentioned that not every
recording is perfectly or optimally balanced....oh, complications. I
don't always provide balance controls. Maybe 1dB of unbalance is
tolerable, but I am not sure about this.
One would think that balance adjusting each way with a remote control
with critical music might be the best way to optimise the sound
including balance.
Anyway, in general my client is happy, and I'll suggest to him that he
place a small strip of masking tape near the balance control which
shows the perfect balance postition after he "measures it in" and then
he won't have to measure again. Gains are virtually identical due to
the amount of local and global NFB.



I'm not sure how he's lined up the axis, because its possible to
arrange the ESL so they partly function as line array speakers, and
ideally the HF path length should remain constant, so the speakers
should be "concave", and made to suit where one sits.

** Correct.

But my client
tells me the sound is utterly awesome, not just able to go loud, but
to go real, and detailed.

** Absolutely correct.

*Listening to a well set up, stacked Quad ESL57s ruins you for all other
speakers.

The system is a plain stereo system, speakers apart and out from room
corners, room maybe 200cu.metres.

** Sounds just about ideal *- *long as the room is quiet and heavily damped
too.


I'm not sure its well damped at all. I don't recall his pics showing
thick carpets and ceiling / wall traps.

The room my friend set up was that sort volume, with carpet lined walls and
a suspended absorber covering about 40% of the ceiling. *Near as dammit to
acoustically dead.

He had a pair of KEF B139s in a large ported box for a sub as well - *sited
behind the listening position at about the same distance away as the Quads.

Awesome sound and all done prior to the arrival of CDs.


My own humble room is 20cu.M, with sloping ceilings and lotsa carpet
and cushions with chopped foam on furniture, Ceilings are sloped and
many room irregularities to minimise having only 3 major dimensions so
that dimensions vary hugely, not favouring any one F too much. So its
a nice room accoustically, and if I get any set of speakers to measure
with a +/- 1.5dB level with pink noise at 3.5M from speakers, those
speakers "travel very well", ie, people like the sound.

In 1976, I just wanted the house I'd bought for $28,000 to have enough
room so that if I swung a cat around by the tail, I wouldn't bash its
brains out anyplace, or let the bugger take the face off me new missus
as the claws went past 'er nose. So I worked me guts out to make the
house bigger. The missus thought it all was dead boring, and she
****ed off, ( and good riddance ! ). So I ended up with a lotta room
at my joint. Had some good parties there, and Jennifer Hawkins has
promised a decor makeover after she moves in next week. 'Bout time.
She's agreed with me over my speakers, Home Brew With Seas and that
size don't matter.

The last cat I had knew exactly where the best stereo image was with
classical. If I put on some rock'n'roll, she'd leave the room.

Patrick Turner.



... *Phil


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