Unity Gain for 12AX7 Stage

[MarshallPlexi]

If I have two channels in parallel (one EF86 and the other 2x 12AX7 gain stages) they should be out of phase with each other when the reach the same side of the PI input. The other side of the PI is connected to the NFB/Presence circuit. I will have an extra half of a 12AT7 left over that I was thinking I could you an another gain stage and invert the signal coming off the 12AX7 channel and get the phasing correct. Does this sound logical?

Using the Triode Calculator here, I found these values for the 12AT7.

Rp - 11k
Rk - 10k (unbypassed)
Rg - 1M
Ri - 470k

Voltage Gain - 1.02
Decibel Gain - 0dB

Think it'll work?

[pdf64]

It will work I think but won't have much output voltage swing. The plate should be sitting about 50-70% of the supply B+, whereas with these values it will be higher than that.
Better to use more usual values and set up regular inverting amplifier with a 1M feedback resistor and 1M series input resistor, see
Designing Single-Stage Inverting Feedback Amplifier
Peter.

[cbarrow7625]

I don't think there is any "ideal" solution for your request. I don't think either of the above suggestions will sound particularly good, I know the inverting feedback amp doesn't sound particularly good (at least not to me, I've tried it). You would probably just be better off building a standard paraphrase PI and come off of the plate. That will also have no gain but it should alloow for "full" voltage swings.

Why do you care if they are in phase? Are you planning on playing through both at the same time? If you are channel switching it shouldn't be a big deal.

[MarshallPlexi]

The channels will be played at the same time and blended. No channel switching.

[Hardtailed]

Just an idea like that: parallel the 12AX7 triodes then use the extra gain stage to get the extra gain level you had with the cascaded stages.

Worth a try?

EDIT: Hehe, just realized that makes no sense... you will still get an inverted signal.
BUT, you could try to parallel the 12AX7 and see if you like that. Might be fun mixed with the EF86 channel