Scott, before abandoning crimps in favor of solder, or swapping out #10
for #2 welding wire, you should be able to actually measure where the
drop is happening. On your bench arrangement, try baring the wire on
either side of one of those crimps and put the voltmeter leads on each
wire - if you've got 0.1volt drop across the connection it'll read
that. To see how much drop is in the #10 wires, put a voltmeter lead on
each end of a wire. Sounds a bit odd to measure the voltage between the
ends of a piece of wire, but it works. The wire is conducting 30 Amps,
but the voltmeter leads are conducting no more than microamps.
Per the 1987 handbook, six feet of #10 has 0.0061 ohms (I'm assuming
your six feet is three feet each way), and at approximately 30 amps,
should be approximately 0.183 volts drop. Notice, however, what that
resistance is - six thousandths of an ohm. Crimp connections can easily
add hundreds, if not tenths, of an ohm. When I pass tens of amps
through connectors, and I care about voltage drops of tenths of a volt,
I always use many parallel pins to reduce the total voltage drop. A
crimp assembly rated at 30A means it won't burn up at that current, but
it does not mean it won't drop voltage. 30A crimp connections are
probably rated assuming 120V or 240V systems, where a 0.5V drop is
negligible. Again, you can confirm where the drop is happening using
your voltmeter.
It's also worth slipping some wires around the pins of the tubes
themselves and then connecting to the voltmeter. The socket contacts
are not without resistance, and many hours of heat can cause oxide
layers to build which increases that resistance. Voltage at the socket
pins on the underside of the chassis is always higher than what the tube
itself sees.
I'm curious what the reflectee's experiences are with 3-500Z sockets.
Most of us seem to understand the risks of crimp connections yet I've
seen little said about socket-to-pin connections, which are also
dependent on pressure-based contact. In my very few years in broadcast
transmitter manufacture, I recall that when one replaced a tube, about
half the time one also replaced the socket due to deterioration in the
finger stock which comprised the filament contact.
73, Dave W8NF
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