[AMRadio] Grounded Grid


wa5bxo at pctechref.com wa5bxo at pctechref.com
Sun Dec 12 19:57:57 EST 2004


It's interesting that you should mention "GG" Don.  I was just talking not long ago with Geoff, W5OMR, about the possibility of GG modulators.  I think the main draw back of this would be an increase in effective plate resistance making damping not as good.  This could be over come with inverse feed back to a predriver stage.  You might need 100 watts of drive to get 1000 watts out but a very high portion of the drive would be included in the output and the linearity should be good.  But wait, there is more!  You would need a larger chassis to accommodate the extra filament XFMR and large driver XFMR.  Hmmm, Could be a job for emitter follower PNP Xsistors as series drivers.  One for each center taps of each filament XFMR.  And a high current medium voltage negative supply to return the collectors to.  
WHAT A CONCEPT.

John, WA5BXO


-----Original Message-----
From: amradio-bounces at mailman.qth.net [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Donald Chester
Sent: Sunday, December 12, 2004 1:37 PM
To: amradio at mailman.qth.net
Subject: RE: [AMRadio] (no subject)


Of course, amateurs have for years used pentodes and tetrodes, including 
807's and 1625's, as triodes in grounded grid linear service.  I have never 
seen the resistor used.  They simply ground all the grids and feed rf to the 
  cathodes.

With 1625's and 807's, a modification is required, to bring the beam forming 
plates out to a separate pin so that it can be grounded along with the 
grids.  This is possible on some brands of tubes.  In others, the bf plates 
are internally connected to the cathode, rerdering them impossible to 
modify.  Without the modification, they are unsatisfactory as g-g amplifiers 
because the bf plates produce undesirable coupling between the input and 
output.

-k4kyv








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