Powerdrive for PP amp with local feedback and pentode driver ?

Jaap · 1st November 2009, 02:53 PM

I plan to build a push pull amp with 807 and 6CB6 tubes with local feedback (see picture, from Glass Audio).
As I have some 2SK2700 lying around I wonder if it could be useful to add the powerdrive concept to this design ?

Gary P · 1st November 2009, 06:27 PM

I've thought of adding a power drive or equivalent circuit to my 1624 local feedback amplifier to allow A2 operation. It should work as long as the input capacitance of the buffer is kept very low. I'm going to give it a shot using the amplifier version of the self bias CCS circuit used as a follower.

Jaap · 1st November 2009, 08:00 PM

Quote:

Originally Posted by Gary P

I've thought of adding a power drive or equivalent circuit to my 1624 local feedback amplifier to allow A2 operation. It should work as long as the input capacitance of the buffer is kept very low. I'm going to give it a shot using the amplifier version of the self bias CCS circuit used as a follower.

I am sure that a lot of fellows here are interested in how this update of the Tabor works out. Keep us informed

wrenchone · 1st November 2009, 08:15 PM

You could always use a triode/pentode combo and use the triode as a follower. This would give you some AB2 capability, just not in full-tilt "George" style...
This is what I'm doing for my "Kingfisher P-P amp, and it still seems sufficient to drive the snot out of the 7591As.

Jaap · 5th November 2009, 09:28 AM

Quote:

Originally Posted by wrenchone

You could always use a triode/pentode combo and use the triode as a follower. This would give you some AB2 capability, just not in full-tilt "George" style...
This is what I'm doing for my "Kingfisher P-P amp, and it still seems sufficient to drive the snot out of the 7591As.

Adding another triode-follower to the 6CB6 gives the opportunity to make it a SLCF a la Rasmussen.
Experts, would this choice be suitable on this place ?

Yvesm · 5th November 2009, 09:58 AM

You may find some inspiration here:
6L6 Push Pull

Should go with 807 as well.

However, I was unable to apply local NFB without experiencing hi frequency instability issues, perhaps too capacitive FB resistors ? ?
Could be a good idea to use multiple resistor in serie because they have very large voltage accross them . . .

Yves.

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1st November 2009, 06:27 PM	#2
Gary P diyAudio Member Join Date: Apr 2002 Location: Portland OR	I've thought of adding a power drive or equivalent circuit to my 1624 local feedback amplifier to allow A2 operation. It should work as long as the input capacitance of the buffer is kept very low. I'm going to give it a shot using the amplifier version of the self bias CCS circuit used as a follower.

1st November 2009, 08:15 PM	#4
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	You could always use a triode/pentode combo and use the triode as a follower. This would give you some AB2 capability, just not in full-tilt "George" style... This is what I'm doing for my "Kingfisher P-P amp, and it still seems sufficient to drive the snot out of the 7591As.

5th November 2009, 09:58 AM	#6
Yvesm diyAudio Member Join Date: Jul 2004 Location: Ardeche	You may find some inspiration here: 6L6 Push Pull Should go with 807 as well. However, I was unable to apply local NFB without experiencing hi frequency instability issues, perhaps too capacitive FB resistors ? ? Could be a good idea to use multiple resistor in serie because they have very large voltage accross them . . . Yves.

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