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RE: high voltage resistors



Original poster: "Mccauley, Daniel H by way of Terry Fritz <teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>


After analysis (by our company's failure analysis department), it was found
that the small interface between the lead
and the resistor was burning up due to the high peak currents running
through them.  I forget the actual term these used for that internal
connection.

We instead used (I said IRC before, but that is incorrect) RCD "PR" type
resistors which worked extremely well under
the same conditions.  However, I do remember when we tried ordering these,
there were very long lead times, even for the most common of values.

But, although manufacturers don't make the carbon composition resistors
anymore, you can still buy them readily.
Check www.alliedelec-dot-com  or www.newark-dot-com.   I know you can buy them from
one of them (at least in bulk).

Dan




That's good to know. Were they duds by chance any of the "high resistance"
resistors ohmite themselves admit are of poor reliability? I was amused when
I say that note on some of their datasheets.

KEN

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, January 21, 2003 10:44 PM
Subject: Re: high voltage resistors


  > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<dhmccauley-at-spacecatlighting-dot-com>
  >
  > Unfortunately, ohmite resistors are very poor for HV pulse applications,
  > even though they may be spec'd to do so.  I recently designed a TWT grid
  > modulator system which in an
  > original design used carbon composition resistors (the old ones.)  Since
  > these resistors have long since been obseleted by all the original
  > manufacturers (although distributors still
  > carry them in stock), we were forced to make a different selection.  We
  > tried all HV pulse type resistors ohmite had to offer, but all failed
  > repeatedly under pulsed load conditions.
  > When I say failed, they failed within 100 hours of  testing.  We ended up
  > going to an IRC pulse duty resistor which proved satisfactory.
  >
  > Dan
  >
  >
  >
  >  > A source of resistors that I sort of gave up on for what I needed is
  > Ohmite.
  >  > They seem to have taken over the victoreen line of HV resistors and
have a
  >  > semi useful online inventory thing that let's you see what distributor
has
  >  > what in stock.
  >  >
  >  > They will make items not stocked just for you, but it's far from
cheap.
  >  >
  >  > www.ohmite-dot-com
  >  >
  >  > KEN
  >  >
  >  >
  >  >
  >  >
  >  >
  >
  >
  >