[Amps] HV transformer buzzing!! Help Please

Sun Jun 10 16:44:53 EDT 2007

Folks:
I was just about to suggest that any potting or sealing of the open frame 
transformer would SIGNIFICANTLY decrease it's heat shedding capability. but 
Carl covers that in his final comment below.

Which raises another question...I have heard that over the long term, the 
failure mechanism of high power, high voltage transformers usually finds 
heat as the antagonist.  What is the mechanism?  I have  felt the core 
frames,  of Kilowatt Amp power supply transformers at the time of heavy 
sustained service, and they are REALLY hot.  That is the outside surface.  
Would the internal core laminations be much hotter?  How hot?   Does that 
kind of heat eventually char inter winding paper insulation wraps, causing 
conductive paths, and failure, or does it maybe melt plastic Bobbins that 
hold and insulate  the widings, also causing failure?

When building amps, or enhancing reilability of commercial (ham)  amps, is 
it a worthy cause to add extra airflow, into/around the power transformer?  
with a  wide selection of cheap, tiny "muffin fans" perhaps you can place 
them strategically near/on/in your power transformer and forstall a 
replacement during your lifetime.
Same... with HV electrolytic caps, any reason to keep cooler?

Another question.  Has anyone quantified the temperatures involved when a 
technician does the "thumb" test by touching a component of an electrical 
device?  I know from experience, say, touching a normal 2 watt resistor in a 
circuit dissipating a couple of watts.  In my opinion, it should be 
uncomfortably warm, say 2 seconds max with my thumb.. that might be normal.  
If I instantly recoil, with an ouch!  I know a clue is there that something 
is wrong, that there is a lot more power/heat there.  I remember in the 
olden days, as a kid, putting my stocking feet on the power transformer of 
my Drake TR-3, under the operating table.  If I was transmitting a lot, it 
was really hot.
So, using all due caution, doing a thumb, or palm test, what might be the 
temps of the following:

Transformer frame, Palm on frame,
Hot, 3 seconds max comfort zone:
Hot  6 seconds comfort zone:

Two watt Resistor (CAREFUL, NOT in HV Circuits)
Mildly warm, 8 seconds comfort zone
Very Warm  3 seconds comfort zone
Hot, 1-2 seconds
VERY HOT, 1/2 second, painful recoil

Sincerely, Pat Barthelow     aa6eg at hotmail.com
http://www.jamesburgdish.org
Jamesburg Earth Station  Moon Bounce Team

http://www.cq-vhf.com
>From: "jeremy-ca" <km1h at jeremy.mv.com>
>To: "W5CUL" <w5cul at sbcglobal.net>, "'Van K7VS'" <wa7fab at cdsnet.net>
>CC: amps at contesting.com
>Subject: Re: [Amps] HV transformer buzzing!!  Help Please
>Date: Sun, 10 Jun 2007 15:27:12 -0400
>
>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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