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Old 23rd May 2007, 04:26 PM   #1
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Question Separate cathode resistors in push pull output


Many thanks to those who helped on my previous question.

Can anyone give me gneral guidance or direct me to a site that discusses replacing the single cathode resistor in a push pull out stage with separate ones and perhaps making them variable to match up as close as possible two unmatched output tubes.

I have both a heathkit and dynaco that are like that.

thank you much

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Old 23rd May 2007, 05:29 PM   #2
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Location: Newark, DE
Through some searching, I've found this thread which seems to discuss the topic to my satisfaction. Pay particular attention to the first dozen posts or so, after that it tends to wander off topic. Also remember the cathode bypass caps are essential to the circuit with separate cathode resistors, otherwise you are seriously screwing with the AC impedance of the outputs.

bias arrangements for P-P amps.

You might take a look at They have an entire forum dedicated to a "build your own" Dynaco ST35 clone. One significant modification to the original Dynaco circuit is the replacement of the common cathode resistor with separate adjustable circuits. I think that is exactly what you are seeking.
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