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Here we go. Even if you just have a direction towards great material to read up on I'd be grateful. Learning the amp tech trade and figured my buddies Peavey Classic VT 410 Series 100 would be a good place to start.

Backstory:
Guitar was warming up on stage, amp went silent.

-If everything is cranked, you can hear some guitar sound, feint at best
-Amp powers on, fuse is good.
-Tested the pre-amp out, it works great minus some old cap noise.
-Swapped the 2 6l6GC tubes for known good ones - no change
-Tubes light up and get plenty warm
-Pulled the "power module" board and reflowed it. - no change
-There's a pretty good hum from the power module/input transformer area
-Nothing is burnt, melted, nor is there any electrical smell
-Pulled the pre amp board, all the solder looks excellent, not even oxidized. I can reflow that if need be, it's a lot.
-All connections have been checked, are tight and de-oxed.
-Verified it's not guitar, cord, speakers, or output jacks.
-Measurements on the OT resistance values B+ to each leg on the Tubes I get 171ohm and 117ohm
-Plate Voltage (Pin 3 to chassis ground) = 514v
-Screen Voltage (Pin 4 to chassis ground) =514v
-The large caps are 350v 100uf. The top one in the photo is the one I question it sees 500v coming in and 253v out.
-The 400ohm resistor on the power module has 514v on either side of it, but when ohmed out reads 400ohm.
-I have no pulled the large caps and checked the uf yet, should that be my next step or are there still other operational checks to be made?

I think that's all I can remember that's been done so far.

I've been a mechanic for many years, but definitely a noob here. I do understand the voltages at play, and cap bleed off.

Any help or direction would be awesome!
Thanks
-Paul

Schematic attached. Though it's a little sketchy as it combines other models with like stuff.