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[Amps] Amp Supply LK500ZB - strange failure mode

Subject: [Amps] Amp Supply LK500ZB - strange failure mode
From: k0zx Rich <>
Date: Thu, 02 Oct 2014 08:59:41 -0600
List-post: <">>
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
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