ASR33 selector magnet driver card

Chuck Guzis cclist at
Tue Mar 20 11:37:17 CDT 2007

On 20 Mar 2007 at 3:48, Mr Ian Primus wrote:

> So - in replacing this component, what should I be
> looking for? The only specification givin is 100A, but
> I see varistors in various places rated in terms of
> Joules or Volts. I don't want to replace the varistor,
> only to have it not give me any protection for that
> transistor.

Well, you know that this is either a 20 ma or 60 ma current loop 
setup, so why not use Ohm's law and compute what the voltage at that 
point should be, then add some for a safely margin, say, 50% and 
select the varistor accordingly?


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