I recently picked up a PR-40 that works perfectly except for, not surprisingly, the necklace reverb.
I've swapped out the appropriate tubes and also tested the drive/return circuits on a digital reverb (which worked fine except for an overabundance of high frequencies that I assume the spring reverb filters out).. so I'm fairly confident both the reverb driver and return circuits are in good working order on the amp. I can also tap on the springs and hear 'thunder' in both reverb channels so the return appears to be working on the reverb itself.
Do these spring reverbs just wear out (i.e. the pickup loses it's magnetism) or is more likely a mechanical issue? Any thoughts? Thanks!