[AMRadio] 4-1000A Grounded Grid Class-C


Bry Carling bcarling at cfl.rr.com
Thu Oct 3 12:04:27 EDT 2013


They often ground the screen too, at least I did with a pair of 4-400A tubes. It was from a fairly common design out of QST or 73.

Bry Carling
http://af4k.com

> On Oct 3, 2013, at 11:58 AM, "Bernie  Doran" <qedconsultants at embarqmail.com> wrote:
> 
> Certainly possible. it would take a bit of driving power. Looking at the tube curves suggest a need for about 240 V RMS swing on the cathode.  I am assuming you are talking about grounded grid for RF, but normal operating voltage on the tube elements.   You also need to modulate the driver stage, usually stated at about 50 to 60 %. It would also need about 150 to 200 Watts of drive.  And there is the need for modulation of the screen along with the plate, numerous ways of doing that.
> 
> Now if you are talking about all grids grounded both for RF and DC, somewhat different. Eimac has approved the 4-1000 for use as  class B in that configuration as long as the plate is at 3000 and above, I have that data sheet somewhere. In that configuration the grid current runs very high, as in near dangerous to the tube.  I strongly suspect that running class C in that configuration would push the grid current into fatal levels.
> 
> A much bigger question is why go to the bother to do this with a 4-1000? I have long considered a pair of 304TLs driven by an 813 as a very reasonable setup, same modulated plate voltage and the 304TLs in parallel, only issue is isolation of the filament of the 304TLs.  A lot of amperes and a lot of voltage swing.     Bernie W8RPW 
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