[Amps] screen grid current dropping

[Jim W7RY]

Perhaps the dummy load drifting causing the loading to change. Try it on an 
antenna on a dead band or borrow a better dummy load.

73
Jim W7RY

----- Original Message ----- 
From: "Carl" <km1h at jeremy.mv.com>
To: "ka1mwp" <ka1mwp at comcast.net>; <Amps at contesting.com>
Sent: Thursday, June 11, 2009 6:30 PM
Subject: Re: [Amps] screen grid current dropping


> It could be a weak tube or some RF component drifting from heating.
>
> Carl
> KM1H
>
>
>
> ----- 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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>


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