[Hallicrafters] HT-37B Tube mystery

[Gary]

Let me throw my two cents worth in here. Being that I have actually been 
inside these transformers (rewinding), I can pretty much update you the REAL 
cause of death. Yes there is insulation failure but something had to cause 
that. This transformer supplies HV and LV and also bias voltage. These 
voltages all come from the same winding, which, is ok in most cases. The 
problem stems from where the low voltage winding ends and ties to the high 
voltage winding. The wire size is smaller. I cant recall at this moment what 
size is used but its pretty small. To small in my book. This smaller size 
wire, along with leaky power supply caps generate to much current draw in 
the winding. This heat will break down the insulation in time and this is 
where your hv to filament supply short occurs. What I have done in the 
process of rewinding is to increase the wire size to match the lv winding. 
This DOES NOT reduce any current draw on the transformer but does help in a 
hv failure. I also use 10 mil nomex between different windings. This seams 
to have had a big effect on transformer life. If you have any other 
questions about transformers, please feel free to email me. I will answer 
them the best I can.
Regards,
Gary...WZ1M
----- Original Message ----- 
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "Jack Schrader" <w1jhs at verizon.net>; "Darryl Jones" 
<1986944 at comcast.net>; <hallicrafters at mailman.qth.net>
Sent: Sunday, April 13, 2008 8:04 PM
Subject: RE: [Hallicrafters] HT-37B Tube mystery


Simply replacing the vacuum tube rectifiers with SS devices does nothing to
solve the problem of transformer failure.  The problem is an insulation
failure between the HV windings and the 5R4 rectifier filament winding.
Replace the 5R4 rectifier with a SS device AND disconnect the 5V filament
leads at the 5R4 socket.  This takes the HV off the 5R4 filament windings.
Don't' worry about the increase in voltage of the HV circuit.  The 6146's
can easily take it.  This does not apply to replacing the 5V4 LV rectifier
with a SS device.  If you do this, you need to compensate  so that the LV
does not change.

David
KC2JD/4

> -----Original Message-----
> From: hallicrafters-bounces at mailman.qth.net
> [mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Jack Schrader
> Sent: Sunday, April 13, 2008 7:43 PM
> To: Darryl Jones; hallicrafters at mailman.qth.net
> Subject: Re: [Hallicrafters] HT-37B Tube mystery
>
>
> According to my 32b the three tubes across the back of the chassis are :
> oa2, 5v4 and 5r4 next to the power transformer.
>
> >From my experience and others, replace the two rectifying tubes(5v4 &
> 5r4) with solid state devices before you burn out the transformer like I
> did. The tranny does not like the combination of a higher line voltage
> and the increase temp developed in the transformer. This same advice
> goes for the ht37.
>
> ----- Original Message -----
> From: "Darryl Jones" <1986944 at comcast.net>
> To: <hallicrafters at mailman.qth.net>
> Sent: Sunday, April 13, 2008 7:30 PM
> Subject: [Hallicrafters] HT-37B Tube mystery
>
>
> Hello All,
>
> I recently picked up an HT-32B and am having problems identifying a
> missing tube. I pulled all the other tubes, and replaced any that my
> Hickock didn't like, but have yet to figure out what the missing tube is
> that wasn't on the chasis. It's located directly behind the tuning
> capacitor on that board, and doesn't have a chasis marking for it.
>
> Anyone have an ID for me?
>
> Thanks for your help,
> Darryl
> ______________________________________________________________
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