[Amps] Alpha 374A problem

[Sam Carpenter]

Could the layers of the xfrmr be coming unlaminated? This is a sound you
might expect to hear if it is happening. I remember on old henry and Collins
amplifiers, loose metal near the xformr or choke could cause something like
that. I also had an AMP SUPPLY LK550 amp that would make that sound under
heavy load. It's transformer was a hypersil on the floor. The sound was
coming from one of the PS PC boards up on the deck not being tightend down
enough.

I would check all of the circuit boards and make sure they are screwed down
all the way tight and you may be able to "clamp" the layers of the
transformer together to rule that out unless it is a replacement hipersil,
which would not do that in the first place.

I am not an expert but have been long enough to see others with the problem
and heard what the fix was. Good luck, Sam N9FUT

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Jeff
Sent: Sunday, March 20, 2011 6:21 PM
To: amps at contesting.com
Subject: [Amps] Alpha 374A problem

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

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