[AMRadio] Millen High Voltage Connectors

david knepper collinsradio at adelphia.net
Mon Jan 9 15:50:26 EST 2006

My homebrew transmitter,  designed by Stan, W3TGR now a silent key,  is 
going through exhaustive and often frustrating testing.  Stan used lots of 
shielded wire - you know the Belden stuff that is deteriorating over time 
with brittle insulation on the wire. I had to replace several leads because 
the center conductor was shorting to ground when the insulation became 
brittle.  So it goes ...

Today, I thought that I had finally debugged the unit - pair of 813's 
modulated by 805's - but I heard the troubling sound of high voltage to 
ground.  Measuring the Millen connectors to ground revealed a short.  Here 
the Millen connectors on the modulator were arcing to ground on the 
secondary side of the modulation transformer running from the high voltage 
through the secondary winding to the PA amplifier.   I am using those light 
tan units that are supposed to be better than the red connectors.  Stan used 
these connectors on the PA amplifier, the modulator deck, and the high 
voltage power supply.

I suppose that under modulation that the peaks exceeded the voltage rating 
of the Millen connectors.  Once before many years ago, I had the same 
problem.  However, these connectors are often used in homebrew construction 
projects as described in the ARRL handbook.

Any ideas out there other than to go with ceramic feedthrough insulators.

Perhaps, it is because of their age and the insulation is breaking down. 
Who knows!


Dave, W3ST
Publisher of the Collins Journal
Secretary to the Collins Radio Association
www.collinsra.com - the CRA Website
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