[Amps] HV transformer buzzing!! Help Please

[jeremy-ca]

Old iron was often built with wood spacers and wedges driven in between the 
core and the laminations. Over time the wood deteriorates and the core 
possibly shrinks a tiny bit from compression of the paper used.
You can buy tapered hardwood wedges at Home Depot and well equipped hardware 
stores as they are used by furniture restorers.

I wouldnt recommend potting as that is rather permanent. If the transformer 
ever fails and you want the original rebuilt then leave it alone. Besides, 
the air circulation is beneficial.

Carl
KM1H


----- Original Message ----- 
From: "W5CUL" <w5cul at sbcglobal.net>
To: "'Van K7VS'" <wa7fab at cdsnet.net>
Cc: <amps at contesting.com>
Sent: Sunday, June 10, 2007 1:19 PM
Subject: Re: [Amps] HV transformer buzzing!! Help Please


> Van,
>
> Transformers will vibrate when voltage is supplied, specifically the
> windings.  This can happen if the primary and secondary windings are not
> wound tightly.  Or if the winding as a whole does not completely fill the
> window of the iron, and thus is a little loose, you can develop some
> buzzing.  I would check the HV transformer for shims (wooden wedges) 
> between
> the windings and the iron core.  If there are no shims, I would make some
> out of wood and place them between the winding and the iron core such that
> the windings are tight within the assembly.  If there are shims already in
> place, then readjust them until the noise is abated.  Now all of this 
> advice
> is without actually seeing the transformer, but from what you describe, it
> certainly has the symptoms of loose windings.  Hope this helps.  I will
> defer to Tom and others if this does not solve your problem.
>
> 73,
>
> Mike
> W5CUL
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Van K7VS
> Sent: Sunday, June 10, 2007 1:14 AM
> To: amps at contesting.com
> Subject: [Amps] HV transformer buzzing!! Help Please
>
> I just finished tearing down and rebuilding a HV/LV supply for a Globe 
> King
> 500A.  Galvanized the chassis and repainted all the xfmrs.  Looks great,
> works great BUT the supply is buzzing quite loudly.  I know it is coming
> from the HV supply on this deck.  LV supply quiet.  The buzz is there when 
> I
> turn on the HV supply switch and become quite a bit louder when I load the
> HV supply down (loading and running the transmitter section).
>
> Any thoughts of what might cause this noise.  I don't think its any kind 
> of
> arcing but a mechanical noise and probably around 60 cycles...maybe.  It 
> is
> low pitched.  This supply using a filament xfmr for the 866A retifiers, a
> 350 ma choke and large High voltage transformer.  I know I have to isolate
> the noise to one of the xfmrs but then what do I do?  Any help/thoughts
> would be appreciated.
>
> Thanks much.  Van, K7VS
>
> PS.  Next step is to clean off the modulator deck, remove all the rust and
> rebuild it.  The RF is pretty clean but doing the same to it.  I fired up
> the transmitter section today and got 300+ watts into a dummy load thru 
> bird
> wattmeter.  Pretty good for an old boy that probably hasn't been on the 
> air
> for thirty or forty years with a very rusty modulation section and very
> rusty power supply deck that now looks like it just came out of the 
> factory!
> HI HI.
>
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