[Amps] Vac Relays for B+

Ian White GM3SEK gm3sek at ifwtech.co.uk
Sun Feb 7 10:44:51 PST 2010

Gary Schafer wrote:

>> The purpose of a properly sized HV resistor is to both limit a tubes 
>>fault  current during an arc but to also survive until the primary 
>>fuse or breaker  does its job.   A true vitreous enamel wirewound 
>>works well for this.
>> OTOH, that tiny resistor can AND WILL sustain an arc under the right
>> conditions and result in some serious damage to other components.

A genuine purpose-designed HV fuses don't look anything like a small 
resistor. That should be telling us something...

>> Carl
>> KM1H
>I agree with Carl. A fuse in the high voltage, whether it be a resistor 
>or a regular fuse will sustain an arc when it opens and can let more 
>energy thru than you want.
>The glitch resistor can not be just any old resistor either. It has to 
>withstand the full high voltage potential of the power supply. When 
>there is a short, full high voltage appears across the glitch resistor. 
>Sometimes more than one vitreous enamel resistors are put in series to 
>get the voltage rating needed.

Yes - and Jim VE7RF had it right too:
## The  big 50 ohm glitch R.. LIMITS the fault current.  The HV fuse, 
INTERRUPTS the current !

That's right: two different components, two different functions.

It's all in Eimac Bulletin 17 <http://tinyurl.com/18r>


73 from Ian GM3SEK

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