>
>One of the principle maladies of my 2x 3-500z HB amp I've acquired is low
>filament voltage at the tube socket--all of 4.3V.
>The filament xfmr is in the main power supply cabinet, going thru a run of
>about 6' of 10AWG stranded. Calculating out the voltage drop for 6' of #10
>at 30A would indicate that I should be able to do this.
>Never believing unknown equipment, first I removed the filament xfmr and
>load-tested it on a bank of 6 parallel-connected 25W/1ohm resistors
>(actually is exactly 5V/30A load!). The xfmr is properly rated (I can get
>4.98V at 29.7A on the resistor bank).
>Bench testing using the 6' run of #10 showed the same voltage drop problem
>as the original installation...only around 4.3V at the resistors.
>QUESTION: The connection from xfmr pigtails to the #10 is via those
>generic lead crimps you get at any electrical outlet. One set was just
>crimped (xfmr pigtails to #10) and one set was actually crimped and
>soldered (#10 to resistor bank).
>Are these lead crimps NFG for 30A work?
Sometimes. . Crimps are not as reliable as soldered connections.
>I just can't believe it's the
>#10...#10 is #10, right?
A pair of #10s has around 60mV drop per foot at 30A.
>PS in the xfmr verification experiment (where I confirmed the xfmr was
>really 5V/30A) I didn't even solder the wires together...just wrapped the
>pigtails and the resistor bank rails (made of #10 also) tight with bus
>wire. I just checked it on a lark to see how much contact resistance there
>was in that arrangement and was quite surprised to see it work out!
>If lead crimps are NFG, what kinds of connectors does one use in 30A
>filament circuits for remotely-mounted xfmrs?
30A-rated connectors with the wires soldered /not crimped/ to the
connector-pins.
- later, Scott.
Rich. Measures. Web site: www.vcnet.com/measures
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