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Re: [Amps] Runaway Plate Current

To: <>, <>, "'Roger'" <>, <>
Subject: Re: [Amps] Runaway Plate Current
From: "Carl" <>
Date: Sun, 29 Dec 2013 10:59:29 -0500
List-post: <">>
OTOH, the NCL-2000 simply removes the screen voltage and hasnt run wild since its 1963 inception and thousands sold.

Im sure many other tetrode amps do the same.
If the screen supply is switched at the wrong point and/or doesnt have a low enough bleeder value it may remain charged long enough to cause problems.


----- Original Message ----- From: "peter chadwick" <> To: <>; "'Roger'" <>; <>
Sent: Saturday, December 28, 2013 5:27 PM
Subject: Re: [Amps] Runaway Plate Current

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
> _______________________________________________
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