[Amps] Pi network tuning

[Tom W8JI]

> Thanks Tom.  The next question is;  Does it matter which 
> side of the blocking capacitor I attach the termination to 
> ground.  This is a 50 mHz amp, and to attach to the anodes 
> would mean long leads. If I hang the resistor at the input 
> to the pi-network, (across C1) the leads can be short.

Mike,

First thing you should keep in mind is the optimum tube load 
impedance, loaded Q, and  the Q you need are all just 
approximations. There isn't any need to get over-precise 
with what amount to a rule-of-thumb. You generally won't see 
a noticeable difference in performance if you are off by a 
factor of two or even significantly more so long as 
operating Q reasonably exceeds the square root of the 
impedance ratios between tube and load in a pi network.

With a 50MHz amp you have to be mindful of distributed and 
stray impedances. The stray capacitance and series 
inductance of tubes, leads, components, and temporary 
connections can have a large effect on 6 meters when 
compared to bands like 40 meters.

What type of tuning cap are you using? Is it a flapper 
plate, a standard variable, or are you relying on tube 
output capacitance? What were the tubes again? How are the 
grids grounded? Are the leads from anode to the tank short 
and wide?

73 Tom