Martin Ryan said:
Hi,
my son has a Mesa Boogie mini rectifier 25, that has developed a buzzing noise from the input transformer area. this is apparent on both channels. All the valves appear to be working properly.
Q, is the transformer on it's way out?
Q, could it be a faulty valve?
Q, or a capacitor, or other failing components?
Any info would be gratefully received.
Cheers,
Martin
Well...
the loop bypass test did not help the situation. Although it is worth a try.
(effects jacks fail frequently, causing similar noises)
From the recording, it reminds me of a break in the signal path, the power amp input being an open circuit...possibly causing the power amp to oscillate.
From the sound of it, and the fact that it is intermittent, and from the fact that it's happening in multiple amps...
I am not concerned about the electricity causing the problem.
You tried changing the tubes,
you tried inspecting the internal connections and jacks...
you bypassed the effects loop, so...you have done almost anything you could have done without test equipment. (good job BTW...)
Now these amps frequently have an FET which mutes the effects loop, and that transistor has been known to fail on other amps.
That is one thing among others that remains.
But until we have a schematic, or until somebody has one on the bench, unfortunately we have run out of simple possibilities.
I believe there is something wrong, I don't doubt it. We just don't have the means so far to find it.
To be continued,
when I have one on the bench, I will let you know whatever I find. Sooner or later I'm going to see one.
FYI
Yes I have been (previously) a Boogie service center, and have fixed many Boogie amps, for many years.
Including fixing several amps, that the factory was unable to fix.
Overall, I am not a novice at repairing Boogies. I am pretty familiar with them.
But it's true that it takes a lot of patience, above and beyond what's required for other guitar amps.