[AMPS] AL1500

[G0MJW]

> Hi ,
> I have a problem with an AL1500 which came on suddenly.
>     The grid current indicated is now showing about three times what it
used
> to.
> The meter even indicates 10ma on cw standby ie no drive.

Rich is probably correct about it being a problem in the valve (tube).
However, do check there is nothing wrong in the metering and PSU circuitry.
I think a leaky cathode bypass cap might produce a similar effect, but so
would a damaged grid current meter shunt.

Depending on how the AL1500 does its supply, there may be some false grid
current indicated, perhaps from an interlock or trip circuit or EHT
measurement. This might only be a mA or so, but if your grid meter shunt has
burnt out, it will appear as much more.


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