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Hi All,

I am putting together a design that would use 2 PIs to feed 2 sets of power tubes in a 36watt platform. These 2 PIs would be setup differently to utilize each set of power tubes appropriately. By this I mean 6V6s need to be driven harder than EL84s, therefore different PIs. The reason I'm thinking about this is that I want a PPIMV for each set of power tubes.

Anyone have any idea if this is easily doable? Any potential gotchas? ANy suggestions of a better way of doing this?

Thanks,
Darin

Darin,

I'm thinking of doing the same thing for my next build. I think this is the only way to do completely independent PPIMVs. The other advantage of this approach is the ability to voice each PI as well. Just make sure you have the inputs of the PIs isolated with a blocking cap.

Good luck

Hey Richard,

So essentially the 2 PIs would be connected in parallel to the output of the pre amp with some value of cap inbetween the grids of each tube. Correct?

What value cap (or range) would work well for this application?

I have been thinking of this as well. What about the OT?

I am thinking of using a 36watt OT, or possibly a JTM45/Bassman OT.

I would think a standard value, like .1 for the 6V6 side for a fuller bass and maybe a .022 or .01 for the EL84 side for a punchier, chrunchier vibe.

Also if you're hooking one channel to one PI and the other to the other PI then you'll need a .1 cap from the "other side" of the PI to ground.

And yes, you can run the power tubes parallel to one 36-50 OT. It looks like a 100 watt amp except you might need to adjust screen resistors ect from each PI to each set of tubes to get the drive right.

Hi Richard,

I would want to connect both pre amp channels to each PI, thus being able to mix the ouput of both sets of power tubes with their respective PPIMVs. I think that his would give me the most tonal variations out of this platform.

One good question here is about channel phase. How do I make sure that each channel is in phase in respect to output. I don't want to have phase cancelation if I A/B/Y between pre amp channels. Do I just count the number of pre amp stages and then connect them to the appropriate side of the PIs so that they are inphase?

Yes, basically you just count gain stages (1/2 a 12ax7) on each channel. If the amount of sides match you're ok. The Trem channel on an 18 would be an exception. One side is used for the oscillator, so you'd only count one stage.

rjgtr wrote:I would think a standard value, like .1 for the 6V6 side for a fuller bass and maybe a .022 or .01 for the EL84 side for a punchier, chrunchier vibe.

Also if you're hooking one channel to one PI and the other to the other PI then you'll need a .1 cap from the "other side" of the PI to ground.

And yes, you can run the power tubes parallel to one 36-50 OT. It looks like a 100 watt amp except you might need to adjust screen resistors ect from each PI to each set of tubes to get the drive right.

Hey Richard,

Just so we are on the same page here, the values suggested above are for the caps between the 2 PIs? So by .1 you mean .1 uf?

Yes .1 uf.