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Re: [Amps] High C out

To: Dennis12Amplify@aol.com, vic@rakefet.com
Subject: Re: [Amps] High C out
From: Bill Fuqua <wlfuqu00@uky.edu>
Date: Fri, 21 Jan 2005 14:40:47 -0500
List-post: <mailto:amps@contesting.com>
For an L you need the capacitance on the high-z side. The capacitance should be from plate to ground and the L in series with the 50 ohm load. Q is the square root of the impedance ratio. You need adjustable L and C to match on all frequencies.

Oddly enough I have seen it used but when I tried it with my 4-1000 I could not get it to work. I will revisit it some time or another. I had hoped to use a L output on my amp and then follow with switched low pass filters which could be use with any of my amplifiers but simplify the amp itself.

73
Bill wa4lav


At 02:03 PM 1/21/2005 -0500, Dennis12Amplify@aol.com wrote:

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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