PP to PPP

amirmk · 8th August 2005, 08:21 PM

What changes other than Transformer ratings (double the mA) and OPT (double the Watts) and heaters should be made when turning a single push pull amplifier to a double one?

ErikdeBest · 8th August 2005, 08:42 PM

To double the power available at the output you will have to halve the impedance of the trafo's primary. Keeping the same impedance at the primary will imply in a lower output impedance (and a greater damping factor as consequence)

With two tubes parallel it's good to have them matched so they drag a same amount of current. If you use fixed bias, use one pot for each tube.

ray_moth · 9th August 2005, 04:17 AM

As stated by ErikdeBest, parallel tubes need half the plate load impedance, as well as double the current from the PS and they should have separate grid bias controls. I've seen some designs for parallel OP tubes that use a small resistor (100 ohm or so) connected in series in each plate circuit, to minimize current-hogging.

Drive signal voltage remains the same, of course, but drive current is doubled, since the OP tube grids are in parallel, grid resistance is halved and Miller capacitance is doubled. This is likely to be more of a concern if the OP tubes are triodes.

845 · 9th August 2005, 07:22 AM

Hi amirmk!
Be on touch- bron1964@bezeqint.net

Michael.

amirmk · 9th August 2005, 10:40 AM

I actually am thinking of doubling triodes (el84 as triodes), does that mean that the driver stage should also be parallel?

ray_moth · 10th August 2005, 11:32 AM

Depends what it's made up of. A low OP impedance driver such as a 12AU7 could probably still do the job. If you have a high impedance driver, such as 12AX7, or a concertina splitter driving the OP tubes directly, it would probably be struggling. .

amirmk · 10th August 2005, 04:32 PM

How low should the output Z be?
A good candidate for this would be an amp with a 12at7 driver?

Michael, have you recived my E-Mail?

845 · 10th August 2005, 05:26 PM

Call me 050-6775168

8th August 2005, 08:21 PM	#1
amirmk diyAudio Member Join Date: Nov 2004 Location: Israel	PP to PPP What changes other than Transformer ratings (double the mA) and OPT (double the Watts) and heaters should be made when turning a single push pull amplifier to a double one?

8th August 2005, 08:42 PM	#2
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	one I know To double the power available at the output you will have to halve the impedance of the trafo's primary. Keeping the same impedance at the primary will imply in a lower output impedance (and a greater damping factor as consequence) With two tubes parallel it's good to have them matched so they drag a same amount of current. If you use fixed bias, use one pot for each tube.

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9th August 2005, 04:17 AM	#3
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	As stated by ErikdeBest, parallel tubes need half the plate load impedance, as well as double the current from the PS and they should have separate grid bias controls. I've seen some designs for parallel OP tubes that use a small resistor (100 ohm or so) connected in series in each plate circuit, to minimize current-hogging. Drive signal voltage remains the same, of course, but drive current is doubled, since the OP tube grids are in parallel, grid resistance is halved and Miller capacitance is doubled. This is likely to be more of a concern if the OP tubes are triodes.

9th August 2005, 07:22 AM	#4
845 diyAudio Member Join Date: Oct 2004	Hi amirmk! Be on touch- bron1964@bezeqint.net Michael.

9th August 2005, 10:40 AM	#5
amirmk diyAudio Member Join Date: Nov 2004 Location: Israel	I actually am thinking of doubling triodes (el84 as triodes), does that mean that the driver stage should also be parallel?

10th August 2005, 11:32 AM	#6
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	Depends what it's made up of. A low OP impedance driver such as a 12AU7 could probably still do the job. If you have a high impedance driver, such as 12AX7, or a concertina splitter driving the OP tubes directly, it would probably be struggling. .

10th August 2005, 04:32 PM	#7
amirmk diyAudio Member Join Date: Nov 2004 Location: Israel	How low should the output Z be? A good candidate for this would be an amp with a 12at7 driver? Michael, have you recived my E-Mail?

10th August 2005, 05:26 PM	#8
845 diyAudio Member Join Date: Oct 2004	Call me 050-6775168

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