Thanks Mark, unless anyone out there has any other ideas, that was the answer I was NOT trying desperately to avoid. It is what I was suspecting myself and I wanted someone to tell me I was wrong. It does sound like a combination of transformer hum (coming thorugh the speakers) and something worse.
Curiously enough there are a few out there at the moment being sold off inexpensively but they sound like power transformers too! (continuously blown fuses)
The electrical buzzing, does it come through the loudspeakers or is it more of a mechanical vibration emanating from the amp/transformer itself? If it's coming through the speakers, I'd look at replacing the (either 2 or 4) large electrolytic power supply filter caps... they definitely DO have a finite lifespan. The power transformer should work forever unless it's asked to provide more current than it is able. Even then there should be a thermal fuse in the windings which would keep the windings from shorting.
Often the most difficult part of this re-cap is sourcing caps which are the proper size and rating. If you have trouble sourcing try posting on AudioKarma or AudioAsylum boards, those guys have a lot of experience with this type of repair.
Well that sounds more hopeful: I thought I had said that the sound does come from the speakers: Apparently not! I might even be able to do it myself if it is just filter caps: They tend to be relatively separate from the rest of the internals. Is it this way in the Carver? And how do I ascertain what the values are? I am in New York where getting unusual caps shouldn't be too impossible.
Unless that model was out of the series Carver made in the 1980's, it doesn't follow standard amplifier designs.
He (Bob Carver) used something he called "Magnetic Field" something or other and the power supply in there isn't like anything you can think of.
Basically they produced amps like the 1.5t where it could output 1200 watts RMS (short term, like 4 or 6 seconds) per channel in a box that weighs around 15 pounds.
The key was the power supply, it used some kind of "loose wound" core and a special triac tied into it somehow that controlled regulation.
Although the caps probably can be found somewhere, I think the problem is the transformer itself. They made buzzing noises in all the models and I beleive it's from whatever they used to gunk the "loose core" inside of it.
I'm saying it's more mechanical than electronic.
I think at this point in time you may only have the choice of finding another M500t which has some other problem and scavenge the transformer out of it.
If Carver is still around it's like so many other companies where it's name lives on but has nothing to do with what it made in the past.
Bob Carver is behind another company called Sunfire but I really don't know if they can or will handle problems with the old Carver stuff. I think this was one of those messy situations where he signed over the patents and technology to the "new Carver" which went into the toilet.
A bit of history with that letter t after the model name, it stands for "transfer function". In the 80's Bob Carver claimed that he could listen to any audio amp and copy the sound characteristics into his amp design making a clone of it.
One audio magazine (Stereophile) took up the challenge and brought him in to listen to some high end, mega dollar amplifier. He listened and tweaked, listened and tweaked more, ending up with a virtual clone of the mega dollar amp. Although the challenge was debated for years, it does seem he accomplished his claim.
Thus all his amps ending with that letter t is supposed to have the same sonic quality (however you want to descibe that) of that mega dollar amp from the challenge.
But this isnt a mechanical sound coming from the transformer, it is an electronic sound coming from the speakers
I've had some experience, years ago, with the Carver PM1.5 type amps. They had a switched power supply via a triac. They also had a voltage adjustment preset. If the power supply voltage was too low you could get constant switching noise from the amps output. Correcting the voltage eliminated the noise.
IIRC the voltages were around + and - 120v, perhaps a bit less - you might want to check the caps' voltage rating and take adequate precautions!
(The PM1.5 used a dual power supply - the 120v supply was switched in to drive additional output transistors when the signal exceeded that of the lower voltage supply. This gave quite good headroom)