[Elecraft] Binding Post Failure (WAS: KX1 s/n 1005 lives!)

[Ron D'Eau Claire]

Many banana plugs and jacks use nylon insulation which is a *terrible* RF
insulator. Nylon is hygroscopic (absorbs moisture) so its insulating
properties are highly dependent upon the relative humidity. 

Running 15 watts into an end-fed wire I literally melted a banana jack that
looks just like those shown at the top of the page here:
http://www.oselectronics.com/ose_p111.htm

In just a few seconds of sending, I smelled hot plastic and saw smoke rising
as the insulation sagged. As it happened, I had a voltage loop (point of
high RF voltage) at the rig on that band and it caused a quick and total
failure. But even at voltages below that which caused failure, part of the
RF was being converted into heat instead of electromagnetic waves. 

All of the Pomona hardware that I've seen uses polycarbonate insulation.
This is superior, tough stuff! Pomona makes these adapters for use with test
equipment at very low voltage levels. The popular 1296 that Matt, K7OE
mentioned, is rated to 500 vac max (see data sheet at
http://tinyurl.com/7mca5). They don't publish dielectric info or mention
their losses at RF, but that sounds adequate for RF power levels up to some
tens of watts into a high impedance (1,000-ohm) load. Of course lower
impedances mean lower voltages. 

I still use nylon banana plugs and jacks for single wire and open wire
feeder connections, even at QRO power levels, but I never rely on the nylon
for insulation. The jacks are always mounted in an acrylic or polycarbonate
insulating panel with ample spaces between them. 

Ron AC7AC