[TMC] XFK - AC leakage to chassis

[jvendely at cfl.rr.com]

Hey Nick,

When the storm has cleared the area, will measure my XFK oven heaters
for comparison. The 200 kc oscillator oven is pretty important if you
want decent frequency stability. I thought both oven heater/thermostat
assys. were the same. If so, you could swap them. BTW, I think the
XFK, GPE-1 exciter, and AFC xtal oven heaters are all the same type...

73,

John K9WT

	-----------------------------------------From: "Nick England" 
To: "tmc"
Cc: 
Sent: Friday July 31 2020 9:58:34PM
Subject: [TMC] XFK - AC leakage to chassis

I started to resurrect an XFK and before applying power checked for
 possible leaky AC line bypass caps - Uh oh - measure about 50K ohms
from AC
 line to chassis. Disconnect the bypass caps and no change. Disconnect
the
 power transformer and no change. Eventually I found that the heating
 elements in the 200kc oscillator oven were the culprit.
 Well, in a device with an ungrounded two wire AC cord, that sure
sounds
 nasty to me.

 I pulled out the heating elements which look like a ceramic tube
within a
 metal jacket that fits into the oven. Yep, 50K from line to that
metal
 jacket .

 The other oven for crystals measures OK. Of course....because I'm
never
 going to use a crystal that one is fine!

 Surely this isn't normal? Has anyone come across this in a TMC oven
before?
 Am I missing some layer of insulation between the heater jacket and
the
 metal of the oven?

 Cheers,
 Nick England K4NYW
 www.navy-radio.com
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