Not in that amp.
----- Original Message -----
From: "Gary Schafer" <email@example.com>
To: "'Paul Elliott'" <firstname.lastname@example.org>; <email@example.com>
Sent: Thursday, February 16, 2012 12:42 PM
Subject: Re: [Amps] 3CX800A7 Grid Current Problem
> Often the plate choke is designed with less than optimum inductance on 160
> and sometimes 80 meters. This is done to avoid choke resonance on the
> With the smaller choke it must be resonant on 160 and that is accomplished
> by using part of the plate tune capacitance to resonate the choke. This
> more current in the choke bypass capacitor. If that capacitor is too small
> or gets warm it will drift and you will get the results that you observed.
> Gary K4FMX
>> -----Original Message-----
>> From: firstname.lastname@example.org [mailto:email@example.com]
>> On Behalf Of Paul Elliott
>> Sent: Monday, February 13, 2012 11:10 PM
>> To: firstname.lastname@example.org
>> Subject: Re: [Amps] 3CX800A7 Grid Current Problem
>> I really didn't know what was the cause of the grid current changing,
>> creeping or rising rapidly, depending on loading, only on 160 m, but it
>> seem that something was heating up and changing with time when the key
>> held down. There was no visual sign of anything wrong in the amplifier
>> output tank section. I decided to change the plate blocking capacitors
>> the B+ bypass cap at the cold end of the plate choke. (relatively easy
>> I replaced the two paralleled 2500 pf plate blocking caps. Nothing
>> I then replaced the 2500 pf B+ bypass capacitor with a 4700 pf (thanks,
>> Carl) capacitor. Now, on 160 m, the amplifier tunes smoothly, and there
>> no change in grid current with a key down 600 watts for three minutes
>> a dummy load).
>> I still don't know exactly what was going on-but am glad the amp is now
>> doing well on all bands.
>> My thanks to all who responded. Your kindness and knowledge are both
>> appreciated very much.
>> 73 Paul W5DM
>> Amps mailing list
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