Sounds decent (ish), no hum/excess hiss but.... When the gain is cranked on the Ultra channel it squeals. Squeal starts a little less than halfway up on the gain pot. Swapped tubes, tried a 5751 in V1 with no luck...
Noticable mods that have been done.... The ribbon cable to V1a has been replaced with individual wires. When I opened it up the grid and plate wires were twisted together, so were the filament and cathode grounds. I unsoldered and un-twisted the wires...no luck. Chopsticking them, the grid/plate wires seem to make a difference but not much....
Looking at the schematic I thought I found something: C11 from the gain pots had a resistor in it's place.....pulled the boards, pulled the resistor.... Hmph, it's a capacitor that looks like a resistor - never seen that before
- turns out Peavey used them a lot. Cap tests fine....On the bottom of the board there is some discoloration of the ground trace around the cap for V1, input jacks and the cap for the filaments. There is also a replacement resistor on the pre-amp tube board for the filaments. Thinking maybe there was a filament issue that burned the ribbon cable. ???
Checked all the grounds around the discolored traces - all test fine. A wire was added to the filament cap but it seems good too.
With no signal plugged in (grounds on input jacks are good) I can see the squeal on both the grid and the plate of V1a. Somehow, when the gain is cranked something is getting back to the grid of V1a.... I think....
Re-flowed solder joints on caps and anything else that looked suspicious - no change. Considering cutting the trace for the greid near the input jacks and adding a shielded wire - haven't tried that yet.
Any suggestions, comments etc. appreciated. Pics and schem attached....
