Low level buzzing coming from tweeters.

The amps are old VTL Deluxe 500's and, though the caps were replaced, there is some transformer hum. I'm wondering if it has just gotten worse over time and is transmitting to the speakers.

Probably not. But depending on how the tubes are lit, if any of the tubes have developed leakage (as measured on a tube tester) that could easily be causing your problem.

I’ve been thinking about the tubes and whether they could be the culprit. There’s about 2200 hours on the power tubes (WingC 6550’s). It will be a chore to test them (12 per amp). I have a B&K 747. Then there’s the small tubes (driver and input, 3 each amp).
Sooo . . . I’m looking at 30 tubes. I guess I’ve got to get myself cranked up to do that.

In the meantime, I’m going to test with a solid state amp (the horror!) just to confirm it is the amps. I’m still a little puzzled over why both speakers have the same issue (the buzz). What are the odds?

@ncarv

If a tube is doing this, it won’t be one of the output tubes. They can make cracking and popping sounds but a low level buzz is unlikely.

@atmasphere 

Thanks for the tip. Saves me from a futile testing regimen.

I’m planning on trying a solid state amp this weekend to rule out possible electrical problem.

Switched the amps between the tweeters & woofers. Buzz was originally from the tweeters. The buzz now came from the woofers, tweeters silent.. Gotta be the amps?