[Amps] RE: 4CX250B Screen Supplies

[Will Matney]

Bill,
The only problem is that the test tone signal is a constant peak to peak 
voltage no matter what the frequency. On the human voice, the peak to 
peak voltage would vary thus varying the current. Now if the test tones 
voltage would be made to vary up and down, it may be made to be close 
but most test equipment I've seen use a constant voltage output. The 
peak to peak voltage changes with the volume in a voice modulated signal 
too. Needless to say, when using the voice, a mere varying of the mic to 
and from the mouth would change the voltage along with the differences 
in the modulated signal of the voice itself. All this being said, the 
signal voltage and current would swing widely as compared to a two tone 
test. This can be verified by watching the peak to peak voltage on a 
scope using both voice and the test tone. The regulator must be able to 
deal with this as you know. Adding capacitance will help the response 
also as you mentioned.

Will Matney


"I disagree. In the two tone situation the screen current is fluctuating 
at the difference frequency of the two frequencies. And if you should 
chose the frequency difference to be the lowest audio frequency 
modulation used (300 Hz usually) you will take in account the bypass 
capacitance reactance. The IMD could be improved simply by having a very 
large AF bypass capacitor having a very low reactance at a few hundred Hz.

73
Bill wa4lav"