>Set up as a tetrode or G.G.?
Grounded grid.
My old ARRL handbook suggests that in G-G, with screen and control grids
grounded and 2500 on the plate, 325 watts is to be expected from a 4-400,
while a 3-500Z at 3kV on the plate is rated for 750 watts.
I suspect that the 4-400 is a poor choice in G-G. I think the problem with
the 4-400 is that if you drive the cathode negative to the point where the
control grid dissipation limit is reached, you haven't got enough volts
between screen grid and cathode to get the peak current that the tube is
capable of - in grounded cathode, you run about 600 volts on the screen of a
4-400. I can't remember why I went for it: I've a feeling that this
particular single band amp was remote controlled, and there wasn't room for
a screen supply. When the HV xfmr gave up ( see last weeks thread on
transformers!) I moved the amp into the shack and ran the HV from the supply
used for the other amp, but didn't bother going back to grounded cathode -
or grounding the screen for RF and raising it positive for DC. Then you'd
need a bias supply..............
By the look of the book figures, anything over a kW for a pair in G-G is
doing pretty well!
73
Peter G3RZP
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|