[Hallicrafters] HT-32 to HT-37

[Gary]

Hi Group:
    Every one has there own view but with all the HT-32/37 transformers I 
have wound, this is what I have found. Every time the HV winding is burned 
up. The LV winding is part of the HV winding along with the bias winding. I 
would say that bad filter caps in either the HV or the LV are causing the 
problem. The insulation in these transformers is far from what I would call 
sufficient. The HV winding heats up, cooks the very thin insulation and then 
shorts to a filament winding. Lets not forget about today's voltages versus 
yester-year voltages. The transformer is reaching saturation at 115 vac on 
the primary so what do you think happens at 122 or 125 volts ac on the 
primary, Lots of current draw and that also contributes to over heating and 
INSULATION FAILURE.
My two cents.
Regards,
Gary...WZ1M
----- Original Message ----- 
From: "David C. Hallam" <dhallam at knology.net>
To: "K4PRF, B. L. Pratt" <pratt at knology.net>
Cc: <hallicrafters at mailman.qth.net>
Sent: Monday, October 01, 2012 3:45 PM
Subject: Re: [Hallicrafters] HT-32 to HT-37


>I think the transformer short problem in the HT32/HT37 transmitters is
> primarily related to the HV 5R4 rectifier rather than the 5V4. The HV
> shorts to the transformer steel through the 5R4 filament winding.
> That's not to say that the 5V4 could not fail and cause a problem.
>
> David
> KW4DH
>
>
> On 10/1/2012 3:26 PM, K4PRF, B. L. Pratt wrote:
>> Lesson learned the hard way.  If you have one of these fine transmitters
>> and if it is still using the 5V4 low voltage rectifier, your power
>> transformer is in danger.  If I remember correctly the problem is caused
>> by a cathode to plate short in the 5V4 which opens the high voltage
>> winding in the PT.  These transformers are very hard to find and
>> expensive if you can find one.  I purchased a beautiful HT-32A several
>> years back knowing that the PT was bad.  I was able to order a
>> replacement PT from the Peter Dahl Co.  Expensive but a perfect
>> replacement and runs very cool.  I replaced that 5V4 with a 5R4 in this
>> and my HT-37.  I am told that those 5V4s have killed many a transformer
>> and some call it a "death tube."  You might while you are in there
>> replace the selenium bias rectifier with a silicon rectifier.  There
>> have been many articles dealing with these modifications on the HT-32s
>> and HT-37s.
>>
>> Burt  K4PRF
>>
>>
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>
> -- 
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> can escape the obligation to pay it.
> Alexis de Tocqueville
>
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