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razorrick1293 4th January 2012 06:28 PM

Parallel SE output
Hi guys,

I know its common to have 2 of the same tube in a SE design, or even similar ones like el84s and 6v6s. but what about different kinds of tubes such as a pentode and a triode? or el84 and 6k6gt? or any thing else if anyone can think of something wilder!

From what i understand the output transformer would see the 2 as one big tube, and as long as they were biased right, everything should be fine, maybe with a 10 ohm resistor connecting the 2 together?

Any comments welcome!


the_manta 4th January 2012 06:48 PM

Regarding CD conditions, you're right.
But more important are the dynamic parameters !
The tubes have for sure very different Ri(Rout) since one is a pentode the other a triode. Differences in transconductance are also a huge problem. The tube with the higher gm will conduct more and more with higher positive drive signal and the other way round with less drive signal. this imbalance in AC-current sharing will cause distortion etc.
The AUDIO-SCULPTURE MAJUSCULE had a related circuit. When big amounts of power were needed, a pentode is "switched" in parallel to the triode with the help of a special circuit. This points into the direction of Class-G/H

razorrick1293 4th January 2012 09:08 PM

Thanks for your reply!

ive just built a circuit which has both el84 and 6v6 output options (including both in parallel) and i switched triode and pentode on both simultaneously. i wasnt sure if i could get away with a t/p switch for each individually.

Ive also just got a 6k6gt to experiment with, and it seemed like it could be a low power replacement for the 6v6.

Distortion is a factor im interested in (for guitar amps) though im also interested in the character it might have in playing music.

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