Power Supply Considerations

[Bob Hardie- W5UQ]

effects of the series resistor can be smoothed out some by using a 
capacitor, like a 50 mFd cap.  So I would take two 100 mFd caps at 500 
VDC each and put them in series with a 100K 2 watt resistor across each 
cap.  Then put the series caps across the HV line OUT of the 750 ohm 
resistor.  The caps will "smooth out" the variations.... some.  At least 
it won't be as bad as it was.
Bob   W5UQ
see W5UQ.com

David C. Hallam wrote:
> 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
>>  had at hand
>> 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
>> tell me about
>> the present circumstance.
>>
>> 73, Alan - KB2HEI
>>
>>
>>
>>
>>
>> **************Planning your summer road trip? Check out AOL
>> Travel Guides.
>>
>>     
> (http://travel.aol.com/travel-guide/united-states?ncid=aoltrv00030000000016)
>
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