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Re: [Amps] Runaway Plate Current

To:, 'Roger' <>,
Subject: Re: [Amps] Runaway Plate Current
From: peter chadwick <>
Date: Sat, 28 Dec 2013 23:27:01 +0100
List-post: <">>
I sent basically the same comment four hours ago, but such are the marvels of 
the internet, it has disappeared. probably resurface ina couple of months.....

But, yes, I totally agree with Gary.


Peter G3RZP

 Message Received: Dec 28 2013, 09:14 PM
 From: "Gary Schafer" <>
 To: "'Roger'" <>,
 Subject: Re: [Amps] Runaway Plate Current
 Are the screens getting grounded when you remove the screen voltage?
 If not that will cause runaway plate current.
 Gary  K4FMX
 > -----Original Message-----
 > From: Amps [] On Behalf Of Roger
 > Sent: Saturday, December 28, 2013 12:16 AM
 > To:
 > Subject: [Amps] Runaway Plate Current
 > 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
 > AI7RR
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