I am working on a Princeton Chorus that was very noisy when the reverb control was turned up. hum, and an occasional crackling noise.

I treated the jacks on the tank with some deoxit D5, and it made no difference.

I removed the reverb tank from the cabinet, and found that someone had been n ther already-the wires from the jacks were soldered directly to the transducers, and the connections were gooped up with silicone sealer.

While I was in there, I discovered 2 things:

-Whoever had the amp before me had the reverb tank plugged in backwards.

-the Output jack on the tank, which is supposed to have it's ground("shell") connected to the metal case of the reverb tank, was severely oxidized and no longer making contact. Shorting the "shell" of the jack to the tank case got rid of the hum, so I scraped a clean spot on the case, and one on the "shell" of the jack, and connected them with a bit of solder(the stock install relied on the "shell" of the jack touching the metal case).

I put everything back together, and now the amp is almost silent with the reverb all the way up.