[Amps] Plate Choke Issue

[Jim Thomson]

Date: Thu, 4 Jan 2018 22:44:46 -0500
From: AJ <iamfromcanadaalso at gmail.com>
To: amps at contesting.com
Subject: Re: [Amps] Plate Choke Issue

<Well

<I hooked up the 50 uhy choke.

<Used some kapton tape to mark some inductance locations on it (10, 20,
<30, 40)

<Txing at 3/4 amp plate current for a minute the choke temps are as
<follows. rf end 145?, 10uhy 150?, 20 uhy 168?, 30 uhy 204?, 40 uhy
<187?, 50 uhy 176? at the B+/bypass caps end. 

<Seems to be warm area, or is it normal to see temp difference along the
<length of a choke? I never measured the temp in the part.

<As measured with a ir thermometer, I do not know the accuracy of the
<unit.

<I measured the temp of the parasitic chokes and resistors, 105?.


<AJ___ VE3HJ

##  I assume this is all in F..and not C  ?    I have never thought of measuring 
the temp along  the length of a plate choke.  Interesting results.  The vac relay may be
heat sinking the cold end of the choke, bringing the temp back down. 
25 gauge wire for the new 50 uh choke is bigger than the typ 27 or 28 gauge used on 
the ameritron choke.   I used  22 gauge on my hb 2 piece chokes, for both the big and 
small chokes.  Although 204 F is hot, with just 750 ma, I suspect when amp is run with more
current, like what one would expect with a 4 x hole amp....into a dummy load of course, that
it could get even hotter.   But for ssb + cw use,  temps would be a lot lower.. vs a 5 min 
dead cxr key down test. 

##  You could, if possible, use bigger gauge wire, and or a slightly bigger diam insulator,
and the bigger gauge wire, like 18-22 gauge for example, may well  drop the temps by a 
bunch.   I have no clue what the typ amp plate choke setup runs for heat, never measured it.
I have only tested on the bench with dc current.    1.5 A  into the henry radio large choke got really
warm.  At 1.75 A, it goes into thermal runaway, and temps skyrocket,  stupid hot.  Toss in  any 
residual RF current, and it could easily get a helluva lot hotter in actual operation. 

Jim   VE7RF