[Amps] IMD levels

[R.Measures]

>I would be more concerned with the transceivers IMD level than the tube. The
>new generation  of radios seem to be spiraling down at an alarming rate.
>Figures of -24 db  below 1 of  2 tones is pretty lousy.
>
>Most Tetrodes  are hovering around -36 db  down on the third order products.
>You have exceptional linear tubes like the 4c1500B, and the 4cx600J which
>have figures in the -40 db range. In the Larger bottles the mighty 4cx10000J
>seems to have a good figure. Although i cant see the point of this tube when
>simply lowering the screen potential of the standard 4cx10000 produces
>similar 3rd order IMD figures with roughly the same output. 

**  The advantage of the ...J over the standard ...D  is that the ...J's 
filament/cathode has c. 7A more peak emission --  if it is ever needed.  
The result is flatter constant-current curves, especially at the low-end 
-- i.e., better linearity.  

>I have never
>been able to  read an explanation  to  what in the tube gives it good IMD
>performance, maybe someone can offer an explanation.

**  It's got something to do with electron-ballistics and having enough 
electrons to do the job at hand.  The nitty gritty is beyond me.  

cheers, Craig.