In a CQ publication, called "New Sideband Handbook", there is an article
titled "The Little Linear". It is the construction article for a small
4CX1000A amplifier. It was one of the many designs of Jo Jennings, W6EI, of
Jennings Radio.
What I was particularly interested in was the construction of the plate rf
choke. It is 100 uh and made of #28 manganin wire. The article has a brief
description on the use of this material. "The output r-f choke for the
plate circuit is made with manganin wire, wound on a form approximately one
inch in diameter and five inches long. The resistance of this material (#28
d.c.c.) produces a very low "Q" and discourages oscillation which could
occur in a resonant choke. The solenoid-type choke has been found to work
very well over the frequency range of the amplifier and does not contain
"holes" that are characteristic of other chokes."
The amplifier covers 10 - 80 meters. I know there were a couple other hams,
who were pretty sharp, who worked for Jennings, so this idea of using the
manganin must have been tested to some degree with no adverse consequences.
I wound one many years ago, but without adequate testing equipment at the
time, never had the nerve to try it out in a live amplifier. It had
significant resistance, which may not have been bad, and would replace the
fixed resistor in the supply recommended by Eimac.
Anyone built an amplifier using such an rf choke, or tested such a choke on
a network analyzer?
73, Colin K7FM
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