>Been reading the threads on input tuning....particularly with regard to
>using the 259. I surely agree with your observation on how things change
>from little drive to max as far as swr is concerned. On the other hand, I've
>had very good agreement on my "T" or "Pi" input pre-tuning exercises when I
>have put small wattage carbon resistor from the cath to ground to simulate
>the loaded condition, per the KD9JQ triode software. In fact, many of my
>amps (even at 6 meters) required very little if any subsequent tuning under
>full drive condx. Anyhow, just thought I'd add my 2C.
Yes, you can get close. You are correct. So it's not a bad
approximation. I designed my input networks using a dummy load of the
same resistance and capacitance that the input of the tube has. It's
sort of an "average" driving impedance. What's interesting is that the
impedance of the tube at low drive and high drive is approximately the
same as the SWR on both is pretty good. It's at mid drive points that
things seem to change a bit. At least on the 4-1000A.
It's also good you are simulating the load of the tube rather than just
using the tube by itself. The reason is cause you'd never drive the tube
into it's active region with the MFJ analyzer. But with the resistors
you are using the impedance that is similar to what the tube will have
when active.
I am posting this to the reflector because you brought up a very good
point.
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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