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[Amps] Plate Chokes.... Yet Again....

To: amps@contesting.com
Subject: [Amps] Plate Chokes.... Yet Again....
From: James Colville <jimw7ry@gmail.com>
Date: Tue, 12 Jan 2010 07:00:32 -0800
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Well I just re-wound an Ameritron plate choke. Actually it was from a
Heathkit SB-1000. It was an old style choke with the continuous winding
scheme (rather than the staggered winding scheme) that had caught fire after
it was used in another amplifier design which was an 8877.

I also have a RF Parts choke here to compare my home wound choke.  I found
some information on the Internet that detailed the actual number of windings
and size of wire supposedly on the Ameritron/RF Parts choke. (Top winding 42
turns, mid winding 55 turns, bottom winding 82 turns). My choke is very
close to the Ameritron/RF parts choke as far as the space the windings take
up on the core.

The re-wind info shows #28 wire which is what I used. BUT my measurements
are different. I measured the wire with my cheap digital micrometer and
found the #28 that I have is slightly larger than the wire on the
Ameritron/RF Parts choke.


Here are the results of my test.


Ameritron/RF Parts   resistance 3.3 ohms  238 uH inductance

My home wound choke  resistance 3.0 ohms and 195 uH of inductance.


Does anyone know what the real size of wire the Ameritron/RF Parts choke is
would with?

I tried to check with a grid dip meter the resonance of the Ameritron/RF
parts choke with both a short and with it open. The bottom of the choke is
marked 11.2 which is I assume the resonate frequency of the choke but it
does not seem to be self resonate there.

I put my home wound choke into my new 8877 chassis and checked the self
resonant frequency and it seem to be around 17 MHz with the choke not
shorted. This new 8877 is not designed for the WARC bands.

Thoughts?
I know... I know.... if catches fire... It was probably resonate in the
wrong place... :)

73
Jim W7RY
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