[AMRadio] Re: 500 Transformer

[Diane Swynar]

Hi Russ,

You speak the truth...

I still have an old Speedy Memo somewhere in my shack library from one of
the Hammond Transformer engineers in Guelph, Ontario, Canada, advising me
to literally BAKE any long-unused, vintage, unpotted transformers in the
oven, to remove residual accumulated moisture BEFORE using them! (or pay
the consequences, Hi Hi).

If memory serves me well, I believe they should be "cooked" upside down, at
about 200 F, for a couple of hours...

It certainly makes sense to me. What I do here to the "end bell" types
with "open" bottoms is pump the insides up clear level with the bottom of
the bells with clear silicone sealant after they've dried. I smooth the
sealant flat at the bottom, so the thing will rest properly on the chassis.
I figure this extra bit of work "seals" the windings, and discorages any
undo tendency to vibrate, as well...

I've done this to about 4 transformers, or so, & have yet to experience any
failure (TOUCH WOOD, Hi Hi).

~73~ Eddy VE3CUI - VE3XZ> 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 <w4qcu at prodigy.net>
>>Reply-To: amradio at mailman.qth.net
>>To: amradio at 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
>> >
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