On Tue, 9 Mar 1999 16:58:43 -0000 Peter Chadwick
<Peter_Chadwick@mitel.com> writes:
>
>Carl says:
>
> >Peter, do you mean completely potting in tar as was done ages
>ago?
> >I have not had or noticed problems with open frame xfmrs that
>are
>vacuum
> >sealed/impregnated.
>
> My failure was a transformer that had no apparent
>impregnation:
>possibly a thin layer of varnish.
> 'Proper' transformers with vacuum varnish impregnation are
>another
>matter, but some of the cheaper
> xfmrs don't bother with that - they just have a lick of
>varnish.
Thats what Dahl does to the mobile CBers..no sealing whatsoever. Those
users are too dumb to realize anyway and just keep ordering replacements.
The
>old 'tar' potting really needs to be a
> vacuum job for best results. Some UK WW2 xfmrs were tar potted
>in
>vacuo: the ones for the Admiralty
> seemed to always be generously rated, with current densities
>in many
>cases of 750amps/square inch.
Not much help when the U -boat sunk the Admiralty's best vessel!
>
> Potted xfmrs do run hotter, but if they are designed for CCS,
>contesting shouldn't bother them.
And thats the rub. Show me any ham amp that has a true CCS rating at its
maximum output. A RTTY ham rating at reduced power is not even close to a
true CCS definition.
Alpha comes close with the 87A but they restrict the output in all modes.
One of
> the UK built amplifiers that ran a pair of 572B's has a
>history of
>the xfmrs failing. The major reason for
> this was that the original design specified 120 deg C
>insulation:
>this was expensive, and buying
> decided on something cheaper under pressure from the boss.
I refused a large order several years ago from a company that wanted
Class H transformers. Some hams are unbelievably cheap and dumb but that
is not expected from a commercial operation.
Shades of Carl's stories of National!!
There are not many of us Nationalites remaining Peter! I still have the
original potted xfmr, that runs very warm, in a NCL-2000 prototype that
I converted to 6M in 1964. Hopefully it will survive 100-150Hr EU QSO
rates again when F2 and Es hits here again.
> If you can get them, mil spec xfmrs in sealed cans full of oil
I prefer sardines in oil myself.
73 Carl KM1H
>are
>the thing......
>
> 73
>
> Peter G3RZP
>
>
Woops, gotta cut off the tails before Bozo wets his undies.
click
click
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