[Amps] RE: 4CX250B Screen Supplies

[Will Matney]

What Rich says is exactly right! The voice can range anywhere in the 
audio spectrum and thus makes the screen current swing widely. The two 
tone test only uses two of the spectrums frequencies and is a constant 
value. Thus, the screen current will be constant and proportional to the 
two incoming tones. Like he mentioned, it wouldn't matter if it was 
regulated or not because it would be set for only those two tones. When 
the human voice is used, I would bet the IMD will raise considerably, 
how much I can not say. A test with a spectrum analyzer would be the way 
to go on this.

Will Matney


Dom --  I also noticed that a two-tone test was used to measure IMD.  A 
voice-test is a better method of measuring IMD since it causes the 
screen-I to vary and the two-tone test produces constant screen-I.   
Other problems with the comparative tests at

>> http://www.ifwtech.co.uk/g3sek/cleansig/imd1.htm
>  
>
was that no comparative dynamic load regulation test was performed on 
any of the screen regulators, and we have no way of knowing how the 
loading was adjusted regarding screen-I before each measurement.  (i. 
e., AB1 tetrode or pentode loading is a major factor here since more 
screen-I = more IMD).
   Also, with a 2-tone test, it would seem not to matter whether the 
screen-V is regulated or unregulated since screen-I is constant and 
therefore screen-V would not vary unless the electric-mains V 
fluctuated.
end

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org