[Amps] Safety choke question

[Jim Thomson]

Date: Thu, 12 Jan 2012 14:01:53 -0500
From: "Carl" <km1h at 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