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? I just can't believe it's the
#10...#10 is #10, right?
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?
Thanks in Advance All...
------------
Scott Townley
nx7u@primenet.com
------------
Collector of:
Stoddard Aircraft EMI/RFI receivers and accessories
Big Parts for that Big Linear Amp
70's era RF test equipment HP/GR/Tek
Radio-related technical reference material 1940+
...anything else that will keep me off the streets at night
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