[Amps] TenTec Centurion - 422 tuning question

Ken Brown ken.d.brown at hawaiiantel.net
Thu Dec 23 16:40:42 PST 2010

> It's also important to realize that a pi-network is an impedance 
> matching network.  So changing the value of the capacitors changes the 
> match between the output impedance of the tubes and the connected 
> transmission line.
When I first read this I thought " Yeah that is pretty important, I sure 
hope everyone talking about amplifiers realizes that."

Then I thought about it a bit more and realized it is only true if you 
interpret the statement correctly. If you meant "the impedance of the 
connected transmission line", that is only true when the connected 
transmission line feeds a load with an impedance equal to that of the 
line. This is a special case, which we typically try to achieve, and 
some are rather fixated on that goal, thinking it is of utmost 
importance. The general case, which is reality when we are tuning the 
amplifier Pi network, is that the Pi-net matches the output impedance of 
the tubes to the impedance presented by the transmission line, which is 
not the same thing (except in the special case) as the transmission line 


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