Back from the amp-atelier.
Swapped the volume outer wires, which made me realise I probably had the tone cap going to the wrong lug of the Vol pot. Well I was partially right.
The tone cap was supposed to go from the Tone-control wiper to ground (ie Lug 1 of the Vol Pot goes to ground). I don't remember doing this, maybe my Amp Sifu is messing with me to see if I'm paying attention or what, but that cap was going to the volume pot's MIDDLE FRICKIN LUG!
Yeesh.
So, rewired that, tidied up and added the wiring to the "ON"-LED, fired it up and...
It worked great, but the Volume pot did nothing. Tone worked. Spin the volume, no change. What?
Unplugged tubes, flipped it upside down and did continuity testing, had my Amp-Sifu check everything — all good. Flipped it upright, plugged the tubes back in (swapped out the preamp for another just 'cuz) and everything worked beautifully. Plugged the original preamp tube back in and ...
Worked perfectly. Zero noise, clear good tone even with cheapo tubes (the original kit's output transformer was junk, so I've got one of Sifu's custom jobbies in the build). Sat the rest of the evening playing, trying to recollect some chord voicings on Sifu's Strat.
Next up, rewire a new preamp-tube socket. Still need a proper rectifier tube, as I was still using some "tone" wood balanced on top of the current rectumfire to make it work — but work it does and how! Voltages, still need to do a complete voltage check. Progress in dribs and drabs.
But wait, there's more... picked up the Tele body (guitar) a friend gifted to me, left at the atelier, brought it home and the neck kickin' around ol' Feral's scratchpad fits like a glove. So that's another project, for another forum and thread.
Dug out the box for the HPF non-pedal build. Will pick out the pieces for that tomorrow.