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Tim Williams
 
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Default Sweep Tube Amp / Design story

A while ago, thanks to Carrol Conklin with the help of Fred IIRC, I have
a tonne of sweep tubes.. unfortunately I don't have any noval or duodecal
sockets so I'll have to buy them later... anyway, here's a new design.

http://webpages.charter.net/dawill/I...LQ6_PP_Amp.gif

After determining the loadline (I really gotta read up on RDH4 and what
they have to say about curved loadlines..) and finding that the tubes
will be within ratings while pushing 80W , I got to work figuring the
driver circuitry. Williamson would certainly work well but that's so
boring, and I figure I can make better utilization of the tubes anyway.
So I thought up an LTP.. something like a 6DJ8 will have enough gain but
then again, I'll want a good 30dB or so NFB (I'll need it on the high
side because the Rp of the sweep tubes is actually quite high) so out
that goes. Maybe pentodes? 3x6AU6, two for the dif. pair, one CCS...
But I don't want to burn 3 sockets just for the driver! Guess I'll
settle with a preamp on the input. Hey, that also solves LTP bias and
eliminates a coupling cap.
The preamp is direct-coupled to the 1st 6DJ8 grid, the opposite grid
AC-grounded. (I can't apply global NFB here because there isn't enough
gain at this point, plus I want to count the preamp stage in the loop.
Otherwise, a differential amp stage such as this would be the perfect
point to apply global NFB in an amp.)

Lesse. Other points on the circuit. Umm:
As you can see I've added the frequency compensation networks, yet to
be determined.
OPT will have to be hand wound since nobody carries anything like that.
(Peak current will be 550mA, hehe I've got a design, and amazingly
the windup comes to like 1/4" of free space on the core.. guess I can
use a few more turns and more interleaving eh?
Adjust 'LTP bias' for 10mA (about 220V on 6DJ8 plates). With any luck,
6EA8 triode should bias to somewhere around 100V plate.
Solid black arrows go to an adjustable -20 to -50V bias supply.
56k and 22k resistors around 31LQ6s are for beam plate bias, presumably
to reduce snivets. Now I'm not building a flyback supply here, but the
data says to have +30V on it, so +30V it shall have. If anyone has any
idea if there's much if any current flowing into these things, let me
know...
Supply. PT will be handwound again, since Hammond only carries one
transformer in this leauge, and its voltage is too high. The way I
figure it, with regulated screen voltage, I don't need much filtering
so I'll just throw on 100uF after the rectifier for filtering. 8Vrms
ripple doesn't bother me much.
Ah yes, the regulator. I'm still thinking about exactly how that'll be,
but it'll have something to do with a 13GF7 (which convieniently has
a .45A heater, so can be connected in series with the 31LQ6s for line
powered heaters Hi Fred . It won't be very adjustable (just needs
to be 125V), but should be good for 50mA continuous, which will only
happen with a full power squarewave output anyway (like, 120Wrms output).

All in all, ya wanna see how it looks? ;-)
http://webpages.charter.net/dawill/Images/31LQ6.jpg
Obviously just a dry layout , with more sweep tubes (in cartons) for
the PT and a small speaker for the OPT. The papers outline the chassis.

Oy.. Thanks for reading this far, unless you just skipped that last
paragraph or two, in which case, you suck! ;-p

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms


  #2   Report Post  
Patrick Turner
 
Posts: n/a
Default



Tim Williams wrote:

A while ago, thanks to Carrol Conklin with the help of Fred IIRC, I have
a tonne of sweep tubes.. unfortunately I don't have any noval or duodecal
sockets so I'll have to buy them later... anyway, here's a new design.

http://webpages.charter.net/dawill/I...LQ6_PP_Amp.gif

After determining the loadline (I really gotta read up on RDH4 and what
they have to say about curved loadlines..) and finding that the tubes
will be within ratings while pushing 80W , I got to work figuring the
driver circuitry. Williamson would certainly work well but that's so
boring, and I figure I can make better utilization of the tubes anyway.
So I thought up an LTP.. something like a 6DJ8 will have enough gain but
then again, I'll want a good 30dB or so NFB (I'll need it on the high
side because the Rp of the sweep tubes is actually quite high) so out
that goes. Maybe pentodes? 3x6AU6, two for the dif. pair, one CCS...
But I don't want to burn 3 sockets just for the driver! Guess I'll
settle with a preamp on the input. Hey, that also solves LTP bias and
eliminates a coupling cap.
The preamp is direct-coupled to the 1st 6DJ8 grid, the opposite grid
AC-grounded. (I can't apply global NFB here because there isn't enough
gain at this point, plus I want to count the preamp stage in the loop.
Otherwise, a differential amp stage such as this would be the perfect
point to apply global NFB in an amp.)

Lesse. Other points on the circuit. Umm:
As you can see I've added the frequency compensation networks, yet to
be determined.
OPT will have to be hand wound since nobody carries anything like that.
(Peak current will be 550mA, hehe I've got a design, and amazingly
the windup comes to like 1/4" of free space on the core.. guess I can
use a few more turns and more interleaving eh?
Adjust 'LTP bias' for 10mA (about 220V on 6DJ8 plates). With any luck,
6EA8 triode should bias to somewhere around 100V plate.
Solid black arrows go to an adjustable -20 to -50V bias supply.
56k and 22k resistors around 31LQ6s are for beam plate bias, presumably
to reduce snivets. Now I'm not building a flyback supply here, but the
data says to have +30V on it, so +30V it shall have. If anyone has any
idea if there's much if any current flowing into these things, let me
know...
Supply. PT will be handwound again, since Hammond only carries one
transformer in this leauge, and its voltage is too high. The way I
figure it, with regulated screen voltage, I don't need much filtering
so I'll just throw on 100uF after the rectifier for filtering. 8Vrms
ripple doesn't bother me much.
Ah yes, the regulator. I'm still thinking about exactly how that'll be,
but it'll have something to do with a 13GF7 (which convieniently has
a .45A heater, so can be connected in series with the 31LQ6s for line
powered heaters Hi Fred . It won't be very adjustable (just needs
to be 125V), but should be good for 50mA continuous, which will only
happen with a full power squarewave output anyway (like, 120Wrms output).

All in all, ya wanna see how it looks? ;-)
http://webpages.charter.net/dawill/Images/31LQ6.jpg
Obviously just a dry layout , with more sweep tubes (in cartons) for
the PT and a small speaker for the OPT. The papers outline the chassis.

Oy.. Thanks for reading this far, unless you just skipped that last
paragraph or two, in which case, you suck! ;-p

Tim


That all ought to keep you off the streets and outa jail
over winter.

The only sweep tubes I like are 6CD6 and 6CM5/EL36.

Patrick Turner.



--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms


  #3   Report Post  
Gregg
 
Posts: n/a
Default

Behold, Tim Williams signaled from keyed 4-1000A filament:

Oy.. Thanks for reading this far, unless you just skipped that last
paragraph or two, in which case, you suck! ;-p


Gah!

You put in that part just for me - I know it :-p

I skipped to the links, looked at the pics and moved on to the next
newsgroup ;-)

--
Gregg
*Perhaps it's useful, even if it can't be SPICE'd*
Visit the GeeK Zone - http://geek.scorpiorising.ca
  #4   Report Post  
Tim Williams
 
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Default

"Patrick Turner" wrote in message
...
That all ought to keep you off the streets and outa jail
over winter.


But the problem is, I need to be on the streets for classes.....

The only sweep tubes I like are 6CD6 and 6CM5/EL36.


Bah, 6CD6 has almost as much heater as plate dissipation, and too high
screen voltage requirement. Go grab some new and plentiful types, with
lower Vsat, Vs and Is and higher Ia, Pd and Gm. :

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms


  #5   Report Post  
Robert Casey
 
Posts: n/a
Default

Tim Williams wrote:

A while ago, thanks to Carrol Conklin with the help of Fred IIRC, I have
a tonne of sweep tubes.. unfortunately I don't have any noval or duodecal
sockets so I'll have to buy them later... anyway, here's a new design.

http://webpages.charter.net/dawill/I...LQ6_PP_Amp.gif

After determining the loadline (I really gotta read up on RDH4 and what
they have to say about curved loadlines..)

Take a look at my page:
http://home.netcom.com/~wa2ise/radios/compaa3.html
It's not hi-fi, but in this AM radio audio amp I discuss loadlines.
About 1/4 way down the page.



  #6   Report Post  
Fred Nachbaur
 
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Default



Tim Williams wrote:
"Patrick Turner" wrote in message
...

That all ought to keep you off the streets and outa jail
over winter.



But the problem is, I need to be on the streets for classes.....


Thought you were home-schooled... ???

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects, Vacuum Tubes & other stuff: |
| http://www.dogstar.dantimax.dk |
+--------------------------------------------+

  #7   Report Post  
doug
 
Posts: n/a
Default

now that would be a great place to use a couple of the ECL84's I have
triode input and then power pentode would make a great LTP with tons of
drive

"Tim Williams" wrote in message
...
A while ago, thanks to Carrol Conklin with the help of Fred IIRC, I have
a tonne of sweep tubes.. unfortunately I don't have any noval or duodecal
sockets so I'll have to buy them later... anyway, here's a new design.

http://webpages.charter.net/dawill/I...LQ6_PP_Amp.gif

After determining the loadline (I really gotta read up on RDH4 and what
they have to say about curved loadlines..) and finding that the tubes
will be within ratings while pushing 80W , I got to work figuring the
driver circuitry. Williamson would certainly work well but that's so
boring, and I figure I can make better utilization of the tubes anyway.
So I thought up an LTP.. something like a 6DJ8 will have enough gain but
then again, I'll want a good 30dB or so NFB (I'll need it on the high
side because the Rp of the sweep tubes is actually quite high) so out
that goes. Maybe pentodes? 3x6AU6, two for the dif. pair, one CCS...
But I don't want to burn 3 sockets just for the driver! Guess I'll
settle with a preamp on the input. Hey, that also solves LTP bias and
eliminates a coupling cap.
The preamp is direct-coupled to the 1st 6DJ8 grid, the opposite grid
AC-grounded. (I can't apply global NFB here because there isn't enough
gain at this point, plus I want to count the preamp stage in the loop.
Otherwise, a differential amp stage such as this would be the perfect
point to apply global NFB in an amp.)

Lesse. Other points on the circuit. Umm:
As you can see I've added the frequency compensation networks, yet to
be determined.
OPT will have to be hand wound since nobody carries anything like that.
(Peak current will be 550mA, hehe I've got a design, and amazingly
the windup comes to like 1/4" of free space on the core.. guess I can
use a few more turns and more interleaving eh?
Adjust 'LTP bias' for 10mA (about 220V on 6DJ8 plates). With any luck,
6EA8 triode should bias to somewhere around 100V plate.
Solid black arrows go to an adjustable -20 to -50V bias supply.
56k and 22k resistors around 31LQ6s are for beam plate bias, presumably
to reduce snivets. Now I'm not building a flyback supply here, but the
data says to have +30V on it, so +30V it shall have. If anyone has any
idea if there's much if any current flowing into these things, let me
know...
Supply. PT will be handwound again, since Hammond only carries one
transformer in this leauge, and its voltage is too high. The way I
figure it, with regulated screen voltage, I don't need much filtering
so I'll just throw on 100uF after the rectifier for filtering. 8Vrms
ripple doesn't bother me much.
Ah yes, the regulator. I'm still thinking about exactly how that'll be,
but it'll have something to do with a 13GF7 (which convieniently has
a .45A heater, so can be connected in series with the 31LQ6s for line
powered heaters Hi Fred . It won't be very adjustable (just needs
to be 125V), but should be good for 50mA continuous, which will only
happen with a full power squarewave output anyway (like, 120Wrms output).

All in all, ya wanna see how it looks? ;-)
http://webpages.charter.net/dawill/Images/31LQ6.jpg
Obviously just a dry layout , with more sweep tubes (in cartons) for
the PT and a small speaker for the OPT. The papers outline the chassis.

Oy.. Thanks for reading this far, unless you just skipped that last
paragraph or two, in which case, you suck! ;-p

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms




  #8   Report Post  
Tim Williams
 
Posts: n/a
Default

"Robert Casey" wrote in message
...
Take a look at my page:
http://home.netcom.com/~wa2ise/radios/compaa3.html
It's not hi-fi, but in this AM radio audio amp I discuss loadlines.
About 1/4 way down the page.


That's a straight, resistive loadline; by curved I mean, the slope goes
up as the opposing tube in the PP stage cuts off (transferring the total
load to just one tube).

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms


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