[Amps] weird grid current

[Carl]

I run a pair of those on 1296 and 2304 and have noticed a bit of drift also 
and it takes quite a bit before power drops. Try it with less drive and 
lighter output loading. Use the minimum drive to maintain the output.

Back bombardment is a likely reason for negative current, its rather common 
in some tetrodes anyway.

Carl
KM1H




----- Original Message ----- 
From: "Gary Patterson" <gpatterson53 at hotmail.com>
To: <amps at contesting.com>
Sent: Saturday, March 05, 2011 9:22 AM
Subject: [Amps] weird grid current


>
>
> I have a 23cm four tube 7289 grounded grid cavity amp.  The four tubes are 
> commonly biased.  It is generating good output.  The strange thing is that 
> on key down for a couple of seconds,  the grid current starts at a 
> reasonable value then goes to zero.  At zero,  I still have full output. 
> I realize its thermal changes that are varying the grid current,  but dont 
> understand full output with no grid current.  Also,  if the amp is miss 
> tuned,  the grid current will go "negative"  (grid meter reads pinned 
> below zero the wrong way).   How can this be??
>
> W4AF
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