[Amps] [AMPS] Drake L-4 negative grid current reading on meter

[Vic K2VCO]

Steve Scoggins wrote:

> A common failure in 3-500Z tubes is a filament to grid short which may be 
> intermittent.
> This type of failure may be detected by the incidence of negative grid 
> current (usually some plate current) during standby. Observing the safety 
> procedures in your manual. Remove the tubes then use a VOM to check the 
> tubes for grid to filament shorts.

It's quite common that these shorts do not appear unless the filament is 
hot. I've seen this several times just on my own and friends' amps. 
Substituting a good tube is really the best test.
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco