[AMPS] Safety resistor

[Vic Rosenthal]

No, Rich, I'm not referring to the glitch resistor.  I know that goes in series
with the plate supply.  I am asking about the one that goes from the negative
power supply output to ground.

73,
Vic, K2VCO
Fresno CA


measures wrote:
> 
> >
> >In the common circuit used for GG triode amplifiers that separates the B-
> >from
> >ground in order to allow for convenient plate and grid current metering,
> >there
> >is a 'safety resistor' from B- to ground.
> >
> >Most designs seem to use a value like 10 or 20 ohms.  As G3sek
> ><http://www.ifwtech.demon.co.uk/g3sek/> points out, if you use the 'voltmeter
> >method' to measure grid current, the high value of the shunt resistor
> >requires a
> >higher value for the safety resistor (he suggests 1000 ohms) to keep the grid
> >metering accurate.
> >
> >My question is:  What malfunction is this 'safety resistor' protecting us
> >against?
> 
> €  Destructive surge current, provided that the resistor is installed
> where it belongs.
> 
> >What could happen if it were omitted or opened in service?
> >
> €    This resistor belongs in the positive side of the hv supply, not the
> negative.  When the glitch resistor is in negative circuitry, a positive
> to gnd arc elevates the cathode circuitry to many kilovolts.  A glitch
> resistor needs to be stout enough to withstand repeated hv positive to
> gnd arcs.
> 
> -  Rich..., 805.386.3734, www.vcnet.com/measures.

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