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!
Thanks
Dave, W3ST
Publisher of the Collins Journal
Secretary to the Collins Radio Association
www.collinsra.com - the CRA Website
Now with PayPal
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