[BC] Assistance With A PI Network Calculation

[Ron Youvan]

<
I was going through my junk box trying to determine what kind
of AM transmitter I might be able to build with available
parts.  I came up with enough parts for a final power
amplifier using three 1625s (12 volt version of the 807) in
parallel.  Wonder if someone could give me the approximate
values of the input and output capacitors for the PI network
at 3.8 MHz?
 >

   A Pi network between the high impedance output of an amplifier
tube/s and the load consists of a "plate tuning" capacitor connected
from the "plate of output tube" (through a DC blocking capacitor)
and ground.  From the junction of the two capacitor the "tank"
coil is connected, the other end of the tank coil is connected
to the load.  The final element the "loading" capacitor is
connected across the load, to ground.
   The pi network is the "impedance transformer" between the output
impedance of the output tube/s and the input impedance of the load
and also provides important "LOW PASS filter" action providing
needed harmonic suppression.
   The variable impedance action can be understood when you realize
the Pi network has two variable capacitors in series across the "tank"
coil, providing a variable auto transformer action.
-- 
    Ron  KA4INM - I think I could live on my pay if
                  governments didn't take half!