Date: Sun, 6 Oct 2019 13:16:21 -0600
From: "Doug Renwick" <ve5ra@sasktel.net>
To: <hzp_electronics@juno.com>, <amps@contesting.com>
Subject: Re: [Amps] Tips For Winding a Plate Choke
<Hi,
<I am looking for tips on how to set up and physically place the wire on the
<form. W8JI omits that information.
<I was hoping that some of the amp gurus here wound a plate choke and would
<share that information, but so far no luck.
<Doug
## Electrician ham buddy across town used a bbq rotisserie. Worked good.
Modified of course. Typ solid 1 inch teflon rod used..with a dimple
dead center
on each end.... or drilled and tapped for .25-20 or .25-28 brass
bolt.
Transverse brass machine screw at each end...to terminate wires. Keep
lower
screw well away from chassis.
## 1 rpm is too slow....it will take forever to wind. 30-60 rpm
works good.
A slowed down drill press will also work.
## The w8ji method for testing works superb....provided the choke is
placed into amp.
Beware, u can buy magnet wire with 3 x different thicknesses of goop on
a given cu wire gauge.
## IF u dont require 12m, life is easier. The original JI choke
had no gaps and resonated
at 10 mhz..and also 20 mhz..and was 320 uh. Choke worked fine on
15M. Bottom gap installed...
and 10 mhz resonance shifted up to 12.5 mhz. 20 mhz resonance
shifted up to 24 mhz. Top gap
installed....and 24 mhz resonance shifted up to 27 mhz. That was the
final config.
## The old B+W 800 choke would resonate just above 21.450 mhz.
Some amps would blow
that choke on 15M. Fix was just to remove 4 turns from top of
choke... shifting the single
resonance up a little higher...... but back then we had no 12m band.
Park the resonance at
23.170 mhz..... and it will work on 15 + 17m .
## another method is to use bigger diam form, if u only have xxx
length to work with.
## still another method is to place 1 turn of .25 inch wide copper
strap around the choke.... and slide it
up and down to shift resonance point or points.
## another scheme is to use 2 x chokes.... with the usual bypass
caps at base of each choke. B+ fed to
base of each choke. spdt vac relay toggles the anode between the top
of each choke. choke 1 is big uh...
like 150-320 uh. Choke 2 is 50 uh. choke 2 is used from 80-10m.
Dead simple.
## a 50 uh choke will resonate at 35 mhz. 50 uh used on the
SB-220. 50 uh also used on buddys
YC-15 amp.... but using 22 gauge wire on hand.
## I tested the ameritron chokes.... and in the DC test jig...will
handle 1.5 A CCS for 2 hrs straight, zero heat.
At 1.7 A ccs.... choke goes into thermal runaway...fast ! Ameritron
choke uses 28 gauge magnet wire.
Jim VE7RF
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