[AMPS] Re: 8875 = 4cx400 ?

[George T. Daughters]

hi again,

> I am courious if any
> one has grounded both grids in the 4cx400 and tried driving it like a
> triode? 

several years ago eimac published an amateur radio application note about 
this mode of operation (AS-1).  the bottom line was ...

big glass tetrodes like 4-125, 4-250, 4-400, and 4-1000 work pretty 
well as triodes, but the "high perveance" tetrodes like 4x150, 4x250, 4x350, 
etc. *DON'T* work well as triodes. their control grids draw huge 
currents... an example was given where the 4x150a had a grid current 
of 1.3 a, screen current was 0.5 a, and the anode current was 0.8 a 
at the peak of the driving voltage.  this is not a "favorable 
distribution" of cathode current.  (it probably makes the 4x150a a 
pretty neat flashbulb... remember them?)

there wasn't a 4cx400 at the time, but i'm betting they are pretty 
poor triode amps!

73, 
k6gt
 

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