[Amps] Alpha 374A problem

[Jeff]

My 374A had been working fine. I went down to the shack and on 15 meters I
get a loud buzzing sound, kind of a cross between a loud buzz and a
vibration.

As I said it had been doing fine, I get this on the Mosley CL-33 as well as
the dipole. output is normal about 800-900 watts. It happens in the Bandpass
position as well as manual tune.

All other bands are fine just a slight hum when transmitting.

 

The next day it seemed ok but then in about 15-20 min. it started again.
Maybe something warming up and going south??? Now it seems to be doing it
most the time.

 

Anyone have any ideas on what could be wrong or where to start looking. I
don't have much experience servicing amps so I'm kind of at a loss as to
where to start.

 

Any advice would be appreciated.

 

Thanks,

 

Jeff, N0OST