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

[Gary Schafer]

Could be loading is too light, drive is too high.

73
Gary  K4FMX

> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Paul
> Sent: Sunday, January 13, 2013 12:30 PM
> To: amps at contesting.com
> 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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