Hi Don: some notes; hope they help. Assuming the amp itself works, the only bugaboo I see is messing with that pickup; gonna need Kap'n or default to chime in but I think the operative principle is impedance matching; how much resistance does the p/u element provide v. how much total impedance the circuit offers; not sure I said that just right but an instrument cable can have an adapter to get to RCA but that's the easy part. Looks like a fun project!
Pickup: if you can open this and put a VOM on it, you can measure the resistance across the element, see how it compares to guitar pickups.
Chassis views top/bottom; encouraging that it isn’t rusted, trashed, or scorched anywhere. All the pieces and parts in plain view are commonly available in the aftermarket; especially the caps and resistors. The can cap can looks like 4-section. Depending on … these can be a nuisance … for lesser men. It will help if unit in there is 1 3/8” dia.; Most 4-section caps are 1 3/8” avoiding punching new holes or mounting loose sections on wiring strips – can be done but a little luck would avoid the need.
Speaker; two voice coils? Must have a crossover in it; Weber has a 6” ceramic in either 4 or 8 ohms; about $30 plus ship. Be nice if an 8” would fit; not sure of out-to-out dimensions for either 6” or 8” Webers.
Switches; lower left in pic looks like turn on for power + volume? contacts in back and pot in front. Center tone? Upper left is interesting; split shaft? The back ½ looks like the body of a slide switch, front like any other pot… ???
The lowest effort / some money / highest chance of success a/k/a not having to tear it apart is cleaning pots (they tell on themselves if they don’t come ‘clean’), fresh tubes, and a new speaker. Everything else requires time…
cj
