[R-390] OT: Humbug transformer

[LEE BAHR]

1.  Shim the core from the laminations with an oak shim if the vibration is 
there.

2.  Remove end bells and hi-pot the transformer (take it to a rewinder. 
Hi-potting is like using a pressure cooker).   Or just submerge the 
transformer in a bucket of polyurethane for a few days so the poly gets into 
all the cracks.  Hopefully it will attach the loose wires to the paper above 
and below it.  It will also attach the core to the laminations.  Then dry 
out and reassemble.

If the transformer is buzzing and there are loose windings, they eventually 
will act as a saw and eat up the paper insulation and eventually short out 
from turn to turn and or from winding layer to winding layer.

Lee, w0vt






----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: <r-390 at mailman.qth.net>
Sent: Tuesday, August 03, 2010 1:01 PM
Subject: [R-390] OT: Humbug transformer


> I've been working on a low-voltage power supply for a while now and am 
> getting to the final assembly stages.
>
> When I bought the transformer for the project, I noticed it had a bit of 
> 60-cycle vibration (hum).  I wanted to avoid the cabinet from becoming a 
> sounding board for the hum so I isolated the transformer on a series of 
> neoprene cushions (sink washers) to both provide a little shock mouting 
> and to minimize the contact area the transformer mounts make with the 
> cabinet.  The cabinet, by the way, is constructed from solid 3/4" red oak.
>
> Last night was the first time I was able to test the mounted transformer 
> and sadly there's still a considerable amount of hum.  It doesn't appear 
> its a sympathetic vibration carried through the mounts to the cabinet but 
> simply the transformer itself sitting there free to vibrate.
>
> Is there any sage advice to cutting down on the hum?  Perhaps since the 
> cabinet is very solid, I should have gone the other way and clamped it 
> tightly to the cabinet and the cabinet would absorb the vibrations?
>
> I realize it's a long shot and I'm either stuck with the hum or replacing 
> the transformer but just thought I'd ask.
>
> BTW, this is an open-frame style transformer.
>
> Thanks,
>
> Barry - N4BUQ
>
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