It is not really unusual for these transformers to go bad. You must
consider the age and how they were manufactured. You can blame
Johnson for using cheaper transformers, they could have used potted
designs. But who would have thought that you would be using this old
stuff? Old transformers do bad things- they suck up moisture in the air
and the windings viberate and break down the
insulation. I don't think you will find anything seriously wrong with
your amp. Heres an experiment: got an old unsealed transformer in
the basement that has not been run in a few years?
Put it in the oven@ 200 degrees. Just leave it in for a few minutes.
Open the oven door and you are likely to see it steaming!
Thats water.....Russ.
From: Dave Aabye <[EMAIL PROTECTED]>
Reply-To: amradio@mailman.qth.net
To: amradio@mailman.qth.net
Subject: [AMRadio] Re: 500 Transformer
Date: Mon, 10 Feb 2003 14:20:22 -0500
Hi Gary,
Yep, it's a bummer!
WZ1M wants $260 to rewind the existing transformer. Peter Dahl sells a
replacement
for $285. I think that Dahl offers a better deal because it is a hypersil
unit
with a 500 ma CCS rating. I believe the original is rated 400 ma ICAS.
Only
drawback is the need for 4 new mounting holes.
I replaced the tube recitifiers with solid state units shortly after
purchasing the
500 (about two years ago). I also inserted thyristers in the primary leads
to cut
down on inrush current. I wonder if you have any further protective
measures to
suggest.
73 de Dave, W4QCU
Oak Ridge, TN
Gary Blau wrote:
> Dave:
>
> Ouch. Sorry to hear that.
> Sounds like WZ1M's offer to rewind might be attractive, unless you can
> find another 500 xfmr somewhere (good luck!). That's a great rig so
> it's worth the investment.
>
> Now, to find out why it went bad in the first place...
> Best of luck.
>
> Gary
> W3AM
>
> Dave Aabye wrote:
> >
> > Hello Gary,
> >
> > Thanks for the suggestion, which I believe has proven to be
conclusive.
> >
> > I hooked my Variac to the primary and slowly increased the secondary
voltage.
> > The caps were disconnect from the rectifiers, so the transformer was
"all by
> > itself". At about 700 volts, the voltage started to jump just a bit.
At
> > maybe 750 v, the secondary emitted a puff of smoke with an
accompanying hiss.
> >
> > I think it is clear that the transformer is shot. Time to call Peter
Dahl!
> >
> > Again, thanks for your input.
> >
> > 73 de Dave
>
> _______________________________________________
> AMRadio mailing list
> AMRadio@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/amradio
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