[Hallicrafters] HT-37 power supply

[David C. Hallam]

I think you started with the wrong supply as you have to consider two power
supplies in the HT-37.  The shorting problems are with the high voltage
supply.  Replacement of the 5R4 with sold state diodes and disconnecting the
5V filaments leads to the socket is something I would definitely recommend.
I've replaced enough power transformers in HT-32/37 not to want to do it any
more.  The extra voltage will not hurt the 6146's in any way and gives you a
slight, I emphasize slight, increase in output.

LV supply is another matter.  In a solid state conversion, I definitely
believe in including dropping resistors to keep the LV at the original
level.  My personal preference is the Weber Copper Cap rectifier.  It
provides the same forward conduction characteristics as the tube and
includes inrush protection.

There is always the argument that applying full voltage to a tube before it
is up to full working temperature will cause stripping of the cathode and
loss of tube life.  This is a consideration in some types of large
transmitting tubes.  With the small transmitting and receiver type tubes in
these rigs, it's not an issue.

David
KC2JD/4

> -----Original Message-----
> From: hallicrafters-bounces at mailman.qth.net
> [mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Robert
> Nickels
> Sent: Friday, January 04, 2008 11:58 AM
> To: hallicrafters at mailman.qth.net
> Subject: [Hallicrafters] HT-37 power supply
>
>
> Thinking about going to solid state rectifiers in the power supply of an
> HT-37.  I know Al Parker and others have recommended this as a way of
> minimizing the potential for transformer shorts from HV to 5 volt
> windings, but I'm also concerned about the increase in voltage that will
> result.    In fact, I did try the LV supply and ended up with over 360
> volts on the low B+ line, which messed up the relay keying tube
> operation.   Putting suitable dropping resistors in series would
> probably generate more heat than the tubes do!
>
> I'm tempted to leave it as-is, with the 5R4/5U4 tubes, but would
> appreciate others experiences.   I just rebuilt the VFO dial shaft
> bearing  with new 3/32" balls; thanks to McMaster Carr for their
> fantastic service - placed the online order at 4:30pm and had parts in
> hand before noon the next day.  I guess it helps to live near the same
> UPS hub.
>
> 73, Bob W9RAN
>
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