[Amps] Amp Supply LK500ZB - strange failure mode

[n8de at thepoint.net]

Sounds like a faulty bias zener.

Don
N8DE

Quoting k0zx Rich <k0zx.co at gmail.com>:

> Wonder if anyone has experienced this failure mode with this or a   
> similar amp:
>
> This amp is 80s vintage and since then has been a solid performer,
> grounded grid with two 3-500z. But it has a developed a problem where
> at power up (no rf drive, ant relay input not active for tx), the plate
> current rises to about 3x normal (about 300ma, 100 is normal), stays
> there for 5 to 10 seconds and then drops to zero.
> If enabled to transmit with  antenna relay input on, plate idle current
> is normal, going from 0 to 100ma.
> If apply rf in, it will output but at only about .6 or .7 its normal output.
> After inspecting the schematic am not seeing an obvious source for the
> problem.
>
> Any suggestions appreciated
> Rich
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