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Old 26th April 2013, 08:31 PM   #1
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Default Wiring a 6AS7G to be Push Pull within its own envelope

Hi All,
I am trying to get some info for a friend, on how to wire a Twin Triode in
a SE 6AS7G Tube Power amplifier. We want to try and wire the tube as Push
Pull in which the two Plates inside will push pull to gain more power and cancel
out the distortion levels! Could that be like Trying to wire a twin triode tube
in Ultra-linear mode? Is this possible to get the Single twin triode power tube to
Behave as if two tubes were used in Push pull output stage? Has anyone ever
tried this? If so, would not the Voltage have to be higher in order to get the current
up to a higher level? Any thoughts would be appreciated! Lydia

Last edited by pianolydia; 26th April 2013 at 08:37 PM.
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Old 26th April 2013, 08:42 PM   #2
TheGimp is offline TheGimp  United States
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Just wire it up as if it were two separate Triodes, which is what it is. They just happen to share a common heater element.

It will be a a triode PP amp.

Here is an example using 6N6P:

http://www.pastisch.se/faktiskt/amp87.gif

And here is an actual 6AS7 one:

Data of 6080pp Stereo Amp.

Last edited by TheGimp; 26th April 2013 at 08:48 PM.
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Old 26th April 2013, 11:19 PM   #3
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One may not get very very high channel separation by this method, often one side can "hear" the other. Otoh this can be a good thing in some cases. Easy to test - just play one channel, dummy load, listen out the other with no input.

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Old 27th April 2013, 02:03 AM   #4
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Quote:
Originally Posted by bear View Post
One may not get very very high channel separation by this method, often one side can "hear" the other. Otoh this can be a good thing in some cases. Easy to test - just play one channel, dummy load, listen out the other with no input.

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Old 27th April 2013, 02:17 AM   #5
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Wiring each tube (both elements in one tube) as one channel will stop any cross-talk issues.
Also note,the 6AS7/6080 (basically the same tube) will require a pretty good voltage swing on the grid,as it doesn't have much 'gain'.
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Old 27th April 2013, 02:19 AM   #6
TheGimp is offline TheGimp  United States
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I can see that being a problem with SE amps where channel separation would matter, but if both triodes in one tube are used in push-pull, how would this matter?
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Old 27th April 2013, 02:37 AM   #7
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oh, yeah, hmmmm... ok well actually it might have an effect as a form of negative feedback! hey! a new invention!!

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Old 27th April 2013, 02:42 AM   #8
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Default It should not matter

Quote:
Originally Posted by TheGimp View Post
I can see that being a problem with SE amps where channel separation would matter, but if both triodes in one tube are used in push-pull, how would this matter?
My thought is that Distortion, would decrease and the signal is sent thru one
side to the other and It should be exactly the same as if one were to use this
as a Push Pull Pair for each channel. I would imagine the distortion to be around
2.8% in full 6-8 watts output pere channel as most of the 2nd Harmonic distortion will be gone. The 6AS7G should be stabilized. It could not hurt to have an Adj. Fixed Bias regulator for biasing these type of tubes in Output stages. Hopefully, We would end up with a 6AS7G SE PP Class A tube amplifier.
I think Stability is Key here. If Noise or crosstalk is involved it should be canceled out in this Push Pull wiring, True? Any thoughts............. Lydia
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Old 27th April 2013, 06:10 AM   #9
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A KISS exemple:

Push Pull 6AS7

Note the "stacked" PSUs:
+400V for the "SRPP-paraphase-splitter-driver" wich provide the huge grid swing the 6AS7's need.
+200V for the power stage itself.

Delivers up to 8W at les than 1% distortion for some 100W total consumption

Have fun

Yves.
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Old 27th April 2013, 06:18 AM   #10
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Cross talk between the two triodes in these is a non-issue. Very low internal resistance, only a few pF of capacitance, and extremely low mu, all means cross talk will be next to nill.

These make great little PP amps, the low rp means the OT can be low impedance, which means relatively few turns and much smaller parasitic inductance and capacitance in the OT.

The only difficult thing with them is the low mu, aim for +-100V drive for the grids. (Actually not that difficult, the low gain gives low miller capacitance which makes them easy to drive)

b+ around 200V, grids at negative 80-90volts is a good starting point.
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