'68 Custom Princeton Reverb hum

[Downshift]

I just got another used '68 Custom Reverb. I've had two others and loved them. This one has a very obnoxious hum in the reverb. It gets louder and louder the more you turn up the dial. My others didn't do this, and its bad enough that I wouldn't be able to mic this amp for a gig.

I've tried common suggestions like tightening loose input jacks, flipping the reverb unit around, etc.

The last thing I can think of is I have one pretty rattly power tube. Could that cause a hum in the reverb?

I ask because I'm willing to spend the money on tubes if it could fix the problem. If it's not a likely fix I don't want to put any more money in the amp. I'll be selling it at a discount if I can't get this fixed quickly.

I'd have to drive into Phoenix to get to an amp tech, and I hate the thought of that drive enough that I'd rather just sell the amp if I can't come up with a quick fix. Any ideas?

 

[Downshift]

Well if anyone is interested, I bought a single tube from a friend to replace the rattling one, and it did not fix the hum.

I've exhausted my desire to fix the problem. Amp is going up for sale at a discount.

 

[Silverface]

If you bought it used on Reverb or eBay you can get your money back and it'll have prepaid shipping. If you bought it locally why haven't you contacted the seller and returned it? Does it have undisclosed modifications? If so, that's grounds for a refund.

Have you done one-by-one tube swaps?

How far are you from amp techs? They are not JUST in Phoenix.

Why have you bought a third one? What happ3ned to the ones you "loved"?

ONE tube swap and you will sell it at a loss? I'm sorry, but that makes no sense.

 

[SoK66]

60 or 120 cycle hum (low pitched or high, almost like a buzz)?