[Hallicrafters] HT-3x transformers

[David Box]

Bob

The failure mode is generally rectifier filament winding to high voltage, or
at least that is the symptom on my HT-37.  Using solid state rectifiers
eliminates the need for the filament winding so you can still use it with
those windings shorted.  I expect that the problem has to do with drying out
of the insulator paper between windings and the location of the taps
associated with these particular windings.  The primary problem with doing
this is the increase in high voltage you are going to get due to the low
resistance of the solid state rectifiers compared to the tube.  You will
also see a slight increase in inrush current on turn on, but a simple
dropping resistor in series with rectifier output fixes that both issues.

If you want to change the transformer out, go ahead and take the step of
ordering a new one from Peter Dahl and put a quality unit back in that you
will not have to worry about.  Taking an old transformer out of a parts
HT-3x  is just asking for the same failure again eventually.  P. Dahl
transformers are not cheap, but they are very well built.

73 de Dave K5MWR


----- Original Message -----
From: "Bob Nickels" <ranickel at mwci.net>
To: <hallicrafters at mailman.qth.net>
Sent: Monday, January 14, 2002 7:56 PM
Subject: [Hallicrafters] HT-3x transformers


> I've always heard that HT-32 and HT-37s were prone to power transformer
failure,
> but I've been lucky.  Can anyone explain what the failure mode is, and why
these
> transmitters seem to fail more often than most?
>
> Is it a good idea to switch from 5R4/5U4 rectifier tubes to solid-state
rectifiers
> in order to reduce the overall current drawn from the transformer?
>
> Thanks and 73,
> Bob W9RAN
>
>
>
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