Thanks for all the info everyone. The circuit is just strait Pi. The C
tune cap backed all the way out unmeshed with minimum capacitance is
where it tuned the best. I removed the C tune vacuum cap and it worked
marvelous but still not optimum. I believe the min. on the cap was
around 15-20pf that I had now removed. The only problem is while it may
tune with just C out capacitance from the tube, I have no way of really
fine tuning now that the C1 is out of the picture. Vic is correct in
that what I was trying to accomplish was an L-Pi. Instead of adding an
inductor from anode to C1, can't I just change the coil dia. and spacing
between C1 & C2 to accomplish the same thing? Or does it have to be in
an L-Pi configuration to cancel out some of the C out from the tube?
Chris
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
On Behalf Of Dennis12Amplify@aol.com
Sent: Friday, January 21, 2005 11:04 AM
To: vic@rakefet.com
Cc: Amps@contesting.com; craxd1@ezwv.com
Subject: Re: [Amps] High C out
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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