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Parallel Triodes

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6/29/2000 11:47 PM

Parallel Triodes

Heya!

I just have a few quick questions for all the tube design gurus out there. I was recently reading over some ideas for modding marshall circuitry, and noticed that one particular modification for increased 'touch sensitivity' was to parallel the first 12AX7 and alter a few components surrounding it. Well, my question is this: What are the advantages of using both sides of a dual-triode in parallel (like the pre-described "touch sensitivity")? How does it affect the important values as the gain of the stage, impedance, etc.? Also, how would one calculate the appropriate values of the new resistors, caps, and such?
I am interested because it seems to me, possibly due to my lack of experience at design, that this may be a way to alter an existing design to achieve things like greater dynamics, at the expense of requiring more preamp tubes. This seems like it may be feasible when you're modifying a design with two or three stages. I was thinking something along the lines of a quasi-trainwreck using three 6SL7's I have hanging around. Thanks!

Sincerely,
Joe

6/30/2000 12:55 AM

This is what came to my mind when I read your post. What I remember hearing involves the non-master amps, and it's just paralelling the inputs of both channels leaving most of the components the same. Just like jumpering the channels without having to actually jumper. Then the two volumes can be used to blend both signal together.

If you want just a single channel, look at the Lightning schem and see what Sampson did there. The values he choose are quite different from paralelling a tube and trying to keep the voicing the same as a single half.

As for the 6SL7, look at the Allesandro Redbone schem. He also builds it with all 6SL7's. That would be some insight into a quasi-Wreck-Fender type design.

I've been thinking about a wreck with the first 3 stages paralelled, into the standard PI output stage. Not knowing enough myself about design I can't figure out when enough is enough.

bw

7/6/2000 2:09 PM
Dennis Claessens	Hi there was a discussion on the effects of paralleling triodes a few months ago. Maybe you can find it with the search option. the gain (mu) of the triode will stay the same; Plate resistance :2, transconductance x2 The output impedance will be lower / the stage can drive the load easier. This might improve tone. Best Regards, Dennis Claessens

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