If you want high vacuum there is little practical difference in pressure
comparing atmospheric pressure to 10^-1 Torr, or 10^-5 Torr. It's close
to 15 psi differential at either vacuum.
A suitable roughing pump (not the little lab pumps you usually see in a
college chemistry lab) should do the job at 10^-1 Torr. Not sure what a
new one would cost nowadays, but they're not cheap. A higher vacuum at
1 X 10^6 Torr is great for high frequency induction heating as 1 X 10^-1
has enough ions left to cause ionization. It looks like the Northern (or
Southern) lights in a chamber. 1 X 10^-7 and higher was used in mass
spectrometers.
Several of us picked up 6 and 12 Liter/min rotary vane pumps that would
easily and quickly reach 1 X 10^-1 on a chamber large enough to hold a
hefty transformer. Even a few 3" and 10" diffusion pumps with cold
traps. Getting the gas out of the internal windings takes a little
longer depending on the transformer construction Some used the combo
for silvering telescope mirrors at 1 X 10^-6.
I'm not sure what use the ones I had were put to, but I gave them to an
active member of the local astronomy club. They all worked, but getting
a leak free system at 1 X 10^-6 took some work.
There is a short learning curve to using a roughing pump with a
diffusion pump as well as the proper diffusion pump oil which does not
like air at the operating temp.
DC704 and DC 705 fluid worked well .In my Tech days I spent many hours
on 2 KW to well over 100 KW induction heating systems. The 100 to 200
KW didn't use vacuum chambers. They used large quartz tubes with the
coils outside and an inert gas (or other mixes) flowing over the load.
They are no longer used and that was 30 years ago
73
Roger (K8RI)
On 9/27/2016 Tuesday 12:01 AM, Bill Turner wrote:
------------ ORIGINAL MESSAGE ------------(may be snipped)
On Mon, 26 Sep 2016 14:40:01 -0400, Carol wrote:
Since the original transformer is totally operational ( voltages and
current) except for the buzzing sound, (probaly due to a lamination
problem), what do I do next?
Do I replace the transformer? Do I get it rewound?
REPLY:
I used to make transformers for the avionics industry and it sounds
like your transformer was not impregnated with varnish completely.
The best way to make them in the first place is to place the
transformer in a vacuum chamber. pull a very high vacuum, flood it
with varnish and repressurize. That drives the varnish deep inside the
transformer and greatly reduces buzzing. Also improves heat transfer.
That's not something you can do at home, but you might try contacting
the manufacturer and see if they can do it for you. Beats buying a new
one.
73, Bill W6WRT
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