12AX7 Distance

[Cliff Schecht]

The P1 extreme, as designed, hits the EL34 (which it was designed around) about as hard as the tube can handle. If you're not using a stock extreme setup (the voltages and specifically the conditions for the tube before the tone stack) are crucial. A 6V6 should be on the verge of being obliterated by the signal, even after the tone stack, in a stock extreme.

If you're not running the eXtreme as intended, with proper voltages throughout, it won't respond like one. It's sensitive in a way most other amps aren't.

Keep in mind the bulk of the distortion you're hearing is from the second preamp stage--even under ideal circumstances, power tube distortion will bury that. You mention an express (predominantly PI clipping) and a plexi (predominatly pi clipping). It's not that power tubes don't distort, but by the time they do, the rest of the circuit is singing over it.

A CF (or SF, if mosfetting) will reduce the insertion loss through the tone stack. However, also try the "jalapeno" tone stack, it's lower insertion loss than the standard, but still intended for a plate driven source.

Additionally, you can try a 12bz7 instead of a 12ax7 for the preamp.

My experiences with SE high gain amps is this (have built quite a few now, 40+). They are very picky about preamp voltages. I have one topology I build with one set of supply voltages (mostly in the preamp stages) that if I get them spot on, the amp will react a certain way that I really like. They can be very touch sensitive when done "right". Since I always use salvaged transformers, the output stage plate voltages can vary quite a bit (300-400V) but as long as the rest of the dropping string is adjusted accordingly I can still get the same touch sensitivity and tone that I'm after.