there is a 220k/100k divider off of the Treble pot wiper. This is just like an old timey MV. If you adjust ratio so that the 220k moves lower in value, while moving the 100k up in value. You can make this thing sound like a Skil saw cutting thru corrugated roofing tin w/ a rip blade, and that's a sound to behold in itself....

anyway, you could put a 500kA pot in place of those resistors to adjust how hard you want to hit the PI
there's PLENTY 'o gain in the first two gain stages that the original design didn't let thru.....actually, too much
the preamp s an ever so slightl variation (almost exact) of the Vox AC30 top boost except it's over filtered (10-12uF is actually enuf rather than the 22uFs).
PI is stock AC15-30, as is output section with the exception of one thing...the screen 2 supply. Only in the Lightning can you run higher than normal EL84 plate voltages w/o risk of frying the '84s. I've used this circuit in a number of '84 powered amps and IT WORKS GOOOOD
Power supply is an over rectified, over filtered AC15.......and that's a good thing unto itself if you like tight amps (think HiWatt...and I LOVE HiWatts)
oh, and instead of a CUT control, it's a post PI MV
but this amp does not sound like a HiWatt or AC15 or an AC30......it sounds like itself
now get to building!!!