-----Original Message-----
From: Jim Strohm <jstrohm@texas.net>
To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: 14 January 2002 00:27
Subject: [AMPS] Input matching experiment
>
>Hi
>
>The latest swapfest yielded up an old ultrasonic generator with an 812A.
>In my stacks of comic boo^H^H^H^H^H^H^H^H^H ARRL handbooks, I find a
>reference that the input impedance of a cathode-fed 811A / 812A is approx.
>300 ohms.
>
>Has anybody ever tried using a broadband matching transformer, the kind
>used in solid-state amps? I'm thinking that a 1:4 transformer would give a
>satisfactory match to 50 ohms; I'm probably going to experiment with a 1:9.
>My idea is not to present a perfect match to the exciter, but to get close
>enough that an SS exciter in the 5-watt range is happy on 10 to 40 meters,
>which is a nice spread for the parts that came with the unit and the space
>I have for a pi network.
>
>Simplicity is the key.
>
>Under load, would the cathode impedance swing higher or lower?
>
>Any comments/words from experience?
>From memory, isn't 812 low mu, better suited to grid drive?
Steve
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|