Well....I've always noticed that there is hum when the reverb is high, so while I wait for a pair of new 6V6 output tubes it seems timely to see what I can do to cure the issue. First off, the stock RCA phono leads are cheap plastic crap, so I will replace with shielded cable and Switchcraft connectors. Taking the tank out and then de-bagging the spring unit it's obvious that the bag has no shielding layer either (do vintage amps have that?). I've put copper tape on cardboard and then covered the tank on top and bottom. Should help. I won't have time to solder up the new cables until next weekend, but fingers crossed that these small mods help. This Princeton wasn't exactly cheap, so I'm struggling to understand why Fender didn't try a bit harder to do the job just that little bit better for us 'Verb hogs.