[Amps] Fwd: Pi-L In-circuit Adjustment Question

[Dennis12Amplify@aol.com]

In a message dated 2/23/05 11:23:15 AM Central Standard Time,  
wlfuqu00 at uky.edu writes:

For  those that have tried the amplifier resonance test, the apparent 
shift in  resonance most likely due to the change of input impedance shift 
of the  input of the amplifier as you change the tune capacitance. You may 
notice  a change in the grid current or exciter to amplifier SWR as you 
change  plate tuning capacitor.



Bill,
 
 When I was doing my testing, I ignored input SWR and grid current  and just 
tuned for maximum power output, and I still had the 'apparent'  shift in 
resonance. And in at least one case, the amplifier was a grid driven  amplifier, 
which also 'negates' the effects you refer to.
 
 Many amplifiers have apparent changes in input SWR as you tune the  output 
tank off peak.
 
 I have a number of theories about why that happens that have nothing  at all 
to do with the tube itself, but rather due to the chassis layout and the  
'shared' ground paths and changes in phase relationships between voltage and  
current between input and output circuits; but that would open up a whole new  
bag of worms, and I don't want to cloud the issues of the existing topic.
 
Regards,
 
Dennis O.