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[Amps] Runaway Plate Current

Subject: [Amps] Runaway Plate Current
From: Roger <>
Date: Fri, 27 Dec 2013 22:16:18 -0800
List-post: <">>
Trying to finish up my 6m Junk Box Amp. Quad 4x150a's, 1700v anode, ~355vdc
screen, ~ -55v bias. Input terminated in 50ohms, output terminated in
50ohms. Keying the amp with no excitation to adjust idle current all goes
well. Idle current adjustable from ~150ma to 400ma +. Screen current is ~
-8ma depending on idle current. Grid Current is 0. As soon as I unkey,
which removes the screen voltage, plate current goes through the roof
forcing an instant shutdown. Anybody have an idea what might be causing this

73, Roger
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