# Power Supply Considerations

David C. Hallam dhallam at RAPIDSYS.COM
Fri Apr 11 09:16:02 EDT 2008

```Alan,

Putting series resistance in the HV supply is not a good idea.  It degrades
the regulation.  However, if you are going to do it, I would use a resistor
rated at 2X what you calculate the dissipation.

David
KC2JD/4

> -----Original Message-----
> From: Boat Anchor Owners and Collectors List
> [mailto:BOATANCHORS at LISTSERV.TEMPE.GOV]On Behalf Of Alan W. Fremmer
> Sent: Friday, April 11, 2008 8:49 AM
> To: BOATANCHORS at LISTSERV.TEMPE.GOV
> Subject: Power Supply Considerations
>
>
> Fellow Restorers/Collectors:
>
> I'm in need of your expertise once again.  I have a Harvey-Wells T-90  in
> need of a power supply.  I decided to try and use what's
> available,  namely a
> Heathkit HP-23B.  The T-90 requires HV B+ of 500-600 volts and LV
>  B+ of 300
> volts.  The power supply provides 820 volts, no load and 700
> volts at 250 ma.  It
> also provides the low voltage B+.
>
> Using a back of the envelope Ohm's Law calculation (I don't recall  what
> parameters I chose) I came up with the idea of putting
> approximately a 500  ohm,
> 25 watt resistor in series with the HV line.  The closest value I
> was 750 ohms.  Well, everything seems to be working but I need  your
> assurance.  Here are my measurements: IR drop across resistor,
> 127  volts, plate
> current at resonance about 100 ma, total current through the
> resistor, 167 ma,
> watts out 60.  The resistor gets VERY hot.  I'm  calculating 20
> watts dissipation.
>
> Would very much appreciate any suggestions as to how to improve
> or modify
> the setup, including getting a power supply with the voltages
> closer to those
> actually needed.
>
> Thanks in advance for your past help and for whatever you can
> the present circumstance.
>
> 73, Alan - KB2HEI
>
>
>
>
>
> Travel Guides.
>
(http://travel.aol.com/travel-guide/united-states?ncid=aoltrv00030000000016)

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