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[AMPS] resistors

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Subject: [AMPS] resistors
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Date: Sun, 21 Feb 1999 09:53:58 -0500

On Sat, 20 Feb 1999 22:47:52 -0800 Rich Measures <>
>>On Sat, 20 Feb 1999 05:43:15 -0800 Rich Measures <>
>>>>  Last time I did this I used a piece of an old
>>>>fiberglass fishing rod (the large end) and ran
>>>>it through the resistors leaving about 3/4" extending
>>>>on each end and then clamped the ends onto standoffs.
>>>> On just about every alpha 77 I've worked on I've found
>>>>some arc damage from the bleeders to the mounting bolts,
>>>>don't like that method.
>>>>Mark  WB8JKR
>>>Ä   Good point.  Through-bolt mtg. also blocks cooling air. 
>>Not if done by the mfgs book.
>?  Through-bolts require some sort of shouldered insulating washer at 
>each end.  this tends to block air from moving through the inside.  

Yes of course but if run at or below rated wattage it will survive.

>>>100k wirewound resistors are known to have a high failure rate.  
>>Details please.
>?  Virtually all of the open failures I have seen or heard about have 
>been in high-values.  Perhaps because the wire used is extremely fine. 

Which is why 100K is the suggested max in any literature I have seen for
bleeders. It also helps to not try and run them at the absolute limit
just to save a few bucks.

I run a pair of 100K 200W in my 2M 4KV supply, runs cool.


>>>If I wanted a Reliable bleeder for a 4kV C-filter supply, I would 
>series up 
>8 to 10 
>>>Matsushita/Panasonic 100k-ohm, 3w MOF resistors on a piece of 
>>>perfboard and be done with it.  
>>Absolute YUK !  800K to 1M way Jose.
>?  What is to be gained by using a 200k-ohm bleeder on a C-filter, 

Quicker HV bleed down time, less chance of a recharge. All my concerns
are safety related and for others not well versed in PS issues.

A string of 3W does not offer much of a voltage breakdown safety margin.
Matsushita not a common distributor item and similar wattage Panasonic,
etc are only 350V.  Going to a 1KV rated Philips AC-03 resistor gives a
comfortable safety margin if such a string is preferred.

73  Carl  KM1H

>R. L. Measures, 805-386-3734, AG6K,  
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