[AMRadio] Amplifier with input drive to screen grid


John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Tue May 23 10:32:15 EDT 2006


Strange indeed Bill!
	I don't mean to be descending but have you checked to see if you
wearing your wife's glasses instead of yours. HIHI 

	It is possible to drive the screens instead of the control grids as
a class B zeros bias circuit however it would require neutralizing to work
properly.  Most folks would opt for the grounded grid configuration where
neutralizing is generally not required.  I can't see where the meter in the
grid circuit would ever show much current unless the rig was once a grounded
grid and then was converted to screen driven and they just didn't change the
grid meter.  Even so 10K in series with the grid meter and no by pass - it
just don't make sense to me.  

	John, WA5BXO

 

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Bill Fondren
Sent: Tuesday, May 23, 2006 7:44 AM
To: AMRadio at mailman.qth.net
Subject: [AMRadio] Amplifier with input drive to screen grid

I recently traded for a linear that has a strange input circuit, at least to
me.  The amp is built in a 18 " Bud rack mount cabinet weighting about 150
lbs.  To heavy for 1 person to handle so I deceided to split the RF deck
from the power supply and put it in a taller cabinet along with the exciter.
No info was with the unit.  I have used it a couple of times and it works
fine .  It uses a pair of 813's in parallel.  I started to draw out the
circuit finding that the drive goes to a tuned circuit and then to the sceen
grids of the 813's.  The control grids are connected together and go to a
10K resistor, the grid current meter and then to grd.  No connection to the
drive circuit at all other than the interelectrode cap. I guess.  The plate
circuit seems to be normal.  Just wondering if any one has seen something
like this before.      Bill     K5PML
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