Help with my new Ampeg V-4

[skot10]

Hello,
My question is simple, which tube on my 1974 V-4 is the phase inverter tube? Also, is is possible to do a mod that I've done on Marshall JCM800's ie adding a cap and a few resistors to the cathode resistor on the first gain stage to increase the gain thus getting an overdriven sound without using a pedal?
Thanks,
Skot

[rf7]

The 12AU7 tube is the PI in the original V-4. Does your amp have the white power and standby switches? If so, it's a later version, and I don't have a schematic for those models. And, yeah you can change the gain in any stage of the amp by changing the cathode resistor and/or capacitor. I usually put a master volume on those amps to get distortion out of them at lower volumes.