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Sounds like tube bias runaway like tubes draw too much current. OPT wire shouldn’t matter if NFB isn’t connected. Dunno if PT side wiring shouldn’t matter that much ’cos there’s distance to signal wires. Output grids are my suspect as I made mistake with connecting grid resistors to bus shared...

Okay, test through 100W light bulb limiter and without tubes, bulb went bright for a second and went quickly dim. Removed limiter and went powering without tubes. No fuses blew, good. Then voltage readings and all good, but all were naturally high without any load. Filaments had 6.7vac and so...

I just finished rebuilding my Simms Watts. Original PCB replaced with sheet metal, made my own ugly layout with improvisation and with bad circuit positioning which I noticed too late. I’m bit ashamed showing it as it’s a mess between strip and p2p layout. Everything looked ok when comparing to...

Megalith Megalith Megalith Megalith And the fifth one is HPF No supporting arguments this time.

Beware dropping dat book as it causes stress on joints and insides pop out from shielding covers… Had to tape my copy back together! :D

Got the idea?

Momentary stop for complaining 70s PCBs and time to bash this sucker down. Like WTF what were they thinking at Peavey about fitting a folded pcb into crammed space? It was just awful getting the pcb out just to replace one leaky eCap. Volume pot had drift and avoided removing PCB with jumpering...

Yeah, cathode bypass was modded at sime point and changed it to back how it was presented in schematic. Played like that for many months and had a hum problem worseninng. Wrong choice! I have 60k grid stops on input jacks, added extra 10k right to grid socket pin. This whole combined grid...

Messing with OT didn’t redeem it, but changing V2b section back to how it was when I got this amp. Maybe preamp tubes at 70s behaved good with cathode arrangement shown at left on the drawing and now it just causes leaky buzzing mayhem? So 50Hz problem solved, but now preamp hiss is audible...

Different caps, few resistors, balanced PI tube, NOS ECC81 and some mechanical stuff for amp maintenance. Sprague caps have hefty 2kV rating and were 1.50€/piece. Not bad.

Amazing work @Hal Harvey Guess I made some progress with my buzzing amp. Opened OT and noticed piece of insulating paper was between shell and outermost laminate. Maybe laminates were just loose and caused some buzz? Couldn’t test it as I noticed cracks in OT legs. Added some metal epoxy putty...

I’ve had clock noise coming through when usied single wall wart supply daisy chained to multiple pedals. The cure was a proper supply unit with truly isolated outputs. So maybe you @Fama should ask how your customer powers his pedal/pedals?

Multiscaling is for the advanced ones who ascend to plane where dimensions won’t restrict. Worrying means we’re not ready.

And here I’ve been wondering this whole day if I should go back to +20uF bypass caps just to make sure nothing unwanted leaks back to signal chain! :D Different topologies, different needs!

I added flyback diodes for my amp, but left out MOVs. Former caused no negative effects on tone! Have you lifted heaters from PI?

How you’re planning to add these? For OT protection?

GUESS WHAT? I found it, finally found it. Measured voltages yesterday and V2b cathode gave odd readings. Today noticed resistor leg had snapped just where it enters into board. That was causing cutoff when raising gain and making resistor move with sound pressure. :D

Re-did HTR wiring for nothing. :D

230-240V/50Hz mains here, but better to mention 60Hz to make it more easy for you weirdos with all kind of wacky wall voltages. Nope, it doesn’t go away without guitar/jack grounded. Added V2a cathode bypass cap to be sure few months old tube isn’t doing heater leakage via cathode, but no use...