How to switch an entire gain stage??

[Mudd]

Thank you Chuck, I have used the MN taper pots for passive guitar circuits. and was thinking exactly that type of taper in this use. I beleive you are correct about the 500k value

[Mudd]

Thanks Helmholtz, the mutual loading effects are running around my head but I do not have enough expertise to know how bet to deal with that. The circuit started from an old destroyed Masco 27 PA amp that I completely gutted and wanted to use the tube compliment but cascading a 6SL7 instead of paralleling it with multiple inputs. I now have a cascoded 6SL7 preamp section with a tone stack and gain pot in between the two triode sections. I tried feeding that output into 6SJ7 pentode then into a 6SC7 PI, from there into a pair of 6L6's push pull. the gain was ridiculous and super noisy (it was just an experiment, LOL). Then tested out with just the Pentode 6SJ7 and 6SL7 feading the PI independently and was happy with both results and different tone potentials. Then came the thought of mixing the two with an MN taper rather than switching them

[Mudd]

Yes, search how Hi Fi amplifier "balance control" is made, or active bass pickup blending.

Basically:
1) you join grids
2) plates are separate, each one goes to its own output volume control.
You have a dual one.
One half (say, the front one) is wired normal, so, say, pentode goes from 0 to max volume when pot swept 0>10
3) triode goes on back half, but wired upside down: 10 is zero volume and 0 is maximum
4) you mix pot wipers with a 220k resistor coming from each one, resistor joint goes to next stage grid.
5) so now 0 means full triode, 10 means full pentode, 5 means "half and half" and so on.
remember to use coupling caps as needed.

There are other ways to do it.

EDIT: best is a custom made pot, half Log ; half anti Log , but those are hard to find and expensive, so next option is using a dual linear pot, because by definition both halves are symmetrical.

Thank you J M, for the detail especially Just a bit concened about the loading effects of tying the grids together. like Hemholz mentioned "Mutual loading effects" or how to minimize them.

[Helmholtz]

Just a bit concened about the loading effects of tying the grids together. like Hemholz mentioned "Mutual loading effects" or how to minimize them.

Maybe you misunderstood. Coupling the grids can be done without any noticeable loading effect as grid inputs are very high impedance. But "connecting" the plates would reduce gain especially of the pentode circuit (having higher output impedance) as the output impedances will mutually load each other and stage gain drops with lower load impedance. And reduced gain also means changed sound/distortion.

So my remark was completely in line with JMF's proposal.

[Mudd]

Maybe you misunderstood. Coupling the grids can be done without any noticeable loading effect as grid inputs are very high impedance. But "connecting" the plates would reduce gain especially of the pentode circuit (having higher output impedance) as the output impedances with mutually load each other and stage gain drops with lower load impedance. And reduced gain also means changed sound/distortion.

So my remark was completely in line with JMF's proposal.

Got it, I misunderstood your first sentence but the second cleared it up, thanks again