I'm hoping someone can help me out with a reverb issue on a 68 Custom Princeton Reverb. There is a really loud humming noise whenever the reverb is on, and above 3 on the dial. When turning it off via footswitch or unplugging the tank cables from the back of the amp, the noise goes away. This leads me to think it is the tank or the cable, but there isn't anything visually wrong with the tank. Does this sound like a reasonable assumption? Or is there something else that it might be? To troubleshoot, is it safe to use the reverb tank from a blues jr? Or will the different size tank do damage when connected to the Princeton Reverb? Thanks in advance for the help!