1965 Supro 6498 "Vibra Verb" - 120hz hum issue

[fdesalvo]

RESOLVED:  The ol' sharing a circuit with the router problem!


Hi, all - hope this note finds you and yours well!


One of these rare beasts landed on my bench and I've got her up and running finally, but there's just one last issue remaining.  I'm working blindly, as there are no schematics of this thing online, so bear with me.  I'm experiencing 120hz hum that's not impacted by any controls or by the removal of preamp tubes.  It only goes away when the power tubes are not present, as you might expect.  I've replaced all electrolytics, save two cap cans which test good according to my ESR meter.  Coupling caps are also new.  Chopsticking the amp reveals nothing.  I've also jumped in new caps to test, but no resultant reduction in buzz.  I'm hoping someone can point me in the right direction.  I have a feeling it's going to be, "Dude the cap cans DUH!". 

[sluckey]

Filter caps are always #1 suspect. Unmatched output tubes can also cause hum.

[fdesalvo]

Steve what’s up brother! Allow me to add another suspect to your list: plugging into an outlet that’s part of a circuit powering a Wi-Fi modem. Resolved!