Re: [Amps] 4CX1500B help needed...high screen current in HF-8020 PA

["Carl" <km1h@jeremy.mv.com>]

The tube needs heavier loading, (less C). In a tetrode the screen current is 
your primary tuning indicator as is grid current in a GG circuit.
Carl
KM1H


----- Original Message ----- 
From: "Paul" <radioboy@telus.net>
To: <amps@contesting.com>
Sent: Sunday, January 13, 2013 12:29 PM
Subject: [Amps] 4CX1500B help needed...high screen current in HF-8020 PA


> Hi Guys,
>
>
>
> I have been struggling trying to figure out why I have high screen current
> in my Collins HF-8020 1KW PA. It uses the 4cx1500B and is an autotune PA
> built like a tank. This one was built in 1990 and I only had it working 
> once
> about 7 years ago, but can't remember if I had any issues then or if this 
> is
> new.  I just reconnected the whole system and it works fine, although one
> day I went to tune it up and I got a fault light for high screen current. 
> I
> went thru a rough alignment of standing idle current, set to 300mA, and
> checked all voltages and this is what I have
>
>
>
> Plate 3000V
>
> Screen 225V
>
> Bias -35 keyed/-75 unkeyed
>
> Standing idle 300mA
>
> Keyed full poop .75A
>
> Screen 40mA  and this is what concerns me. The fault light is off now but 
> it
> is still way high, I think. Should it be about 15mA?
>
>
>
> Anyway, any help would be appreciated. The tube is NOS 1983 with very few
> hours on it. All relays, contacts, switches and everything I can see
> mechanically is spotless inside.  I do have full manuals for this and have
> read thru them but holy cow, they read like a science lesson. I'm sure I
> could eventually figure it out after weeks of reading and studying...It 
> does
> put out full power no problem, over 1KW.
>
>
>
> Any help would be greatly appreciated.
>
>
>
> 73
>
> Paul
>
> VE7KHz
>
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