In a message dated 1/21/05 12:49:50 PM Central Standard Time,
vic@rakefet.com writes:
Nope, he's talking about adding some inductance between the plate and the
tune-C, making a kind of "L-Pi" (or L-Pi-L!) network. The idea is that with
very high plate load impedances it may be impossible to get a low-enough
minimum
capacity in the tune-C to permit a reasonably low Q. Adding some inductance
before the Pi network pre-transforms the load impedance to a lower value so
a
practical capacitor can be used.
I agree.
He's creating a two stage impedance transformer.
I'm sorry but I consider a Pi network a Pi network no matter which end is
connected to where; and I know that the large C is on the low impedance side
of the impedance transformer. I did't realize I was in error calling it
a Pi-L
network instead of an L-Pi network, but I guess I can see where some may get
confused. I DID state that the PLATE C became the new TUNE C in that
configuration.
I have used it myself in some cases to UP-CONVERT impedances to obtain a
reasonable tank Q.
A good example being multiple sweep tubes in parallel where the
total plate
capacitance is greater than 50 PFD. I have also used similar circuitry to
match the Collector impedance from the output of a single ended transistor
amplifier before we started using broad band transformers to do the
impedance
matching, but once again that was for converting a low impedance to a
higher one.
Dennis O.
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