>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.
This is the grid current meter shunt resistor. It must have glitch
diodes across it to protect it from hv to gnd arcs so it can not be a
"safety" device. Typical values are around 1-ohm.
>
>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.
- Rich..., 805.386.3734, www.vcnet.com/measures.
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