[Amps] screen grid current dropping

Carl km1h at jeremy.mv.com
Thu Jun 11 18:30:00 PDT 2009

It could be a weak tube or some RF component drifting from heating.


----- Original Message ----- 
From: "ka1mwp" <ka1mwp at comcast.net>
To: <Amps at contesting.com>
Sent: Thursday, June 11, 2009 6:33 PM
Subject: [Amps] screen grid current dropping

> Well, here is one I can't seem to figure out easily..
> My GU-84b amp with 2100v plate, -65 on control grid, 365v on screen
> grid, have a meter monitoring the
> Screen current.
> I watch this current go from .7ma idle to 25ma at 1kw key down..(can't
> do this long on the oil filled dummy load)
> The current drops from 20 or so ma down thru 12 with the voltages and
> output watts staying pretty close to values.
> I'm using the tetrode boards and have it setup as in the manual..only
> slight component value changes for the screen
> Resistors to get correct volts out, which is rock solid at 365vdc.
> Clues to look at?
> The schematic I posted on the site is pretty close to what I have.
> http://home.comcast.net/~ka1mwp/gu84b_new_sch_rev4.JPG
> thanks for any help in the search.
> Chuck
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