Date: Thu, 12 Jan 2012 14:01:53 -0500
From: "Carl" <km1h@jeremy.mv.com>
Subject: Re: [Amps] Safety choke question
A 1MH 300ma piewound choke should be just fine in normal operation and still
give the amps fuse time to react. Just don't use some slow clunky breaker.
Carl
KM1H
## That's 70's arrl book fubar. At the VE7ZZZ MM contest site, in the 80's...
a plate
block cap let go.... and the 2.5 mh piewound choke literally vapourized. That
was on a hb
4-1000 amp..with 5.5 kv and a pair of small oil caps. No glitch R was used
either.
A typ breaker, if sized right, [thermal type,not the faster mag hydraulic
type] will open off in
35 msecs, with a dead short. The ga used in those small 300-500ma pie wound
chokes is tiny stuff.
This is yet another reason to use a 50 ohm, heavy duty glitch R, and also a
fast HV fuse, in the B+ line.
## I checked several of those pie wound chokes..and a lot of em are 25-40 ohms
dc resistance. The
2.5 mh grid chokes I pulled from the drake L4B's are only .915 ohm...go
figure.
## after a 2nd pie wound choke grenaded itself, that was it.... no more pie
wound chokes. I looked at
a few commercial 10 kw amps..and they all used a 45 uh single solenoid choke,
wound with 16-18 ga
magnet wire. The torroid types wound with 12 ga magnet wire also work fine.
The single layer solenoid
variety are easy to fabricate..with just some 1" diam solid teflon rod..and
18 ga magnet wire.
Later... Jim VE7RF
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