This is a tube amp with about 400VDC available on the B+, you could easily kill yourself trying to service this amp if you don't know what you are doing and follow high voltage safe working guidelines. If you haven't given up yet, make sure you discharge the power supply filter caps before doing anything else. If you have any question at all regarding the previous statements, just give up and take it to a qualified technician.
You should be able to find a suitable schematic diagram online - try el34world.com.
Drain the power supply filter caps and lube the pots with "Lock Ease". The solvent will clean the pots, while the graphite powder fills in microscopic voids in the resistance path. If any pots are still noisy, replace them.
Next, to diagnose the reverb... you can see if the driver tube and transformer are ok by just connecting an 8ohm speaker in place of the reverb tank "in" and playing a few notes. If you get no noise there, focus on V3 (12at7) and T1 .
If you do get noise there, reconnect the reverb tank input and attach the reverb tank output to a spare practice amp, or a phono input on a stereo, see if you get sound out of the tank.
If the tank is OK, and the driver side is OK, and you are sure the cables to and from the tank are fine, then try replacing V4 (12ax7).
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