Hi Mike
I think all the wire sizes you mentioned are too large, and the resistor
might be right on the edge dissipation wise. I just went through this,
and reduced the filament voltage on my Henry 3K, which has a 7.5v
filament at 21.5amps that was running at 8.05 volts. It has 5 voltage
taps on the discreet filament transformer, but it still was too high. I
solved the problem by inserting a 12" piece of #22 TEFLON COATED wire
in EACH filament transformer secondary lead, for a total of 24". That
was found by trial and error (only took 2 tries, found the voltage drop
with 3" of wire, and then calculated the necessary length. Hit it right
on the money.)
So, for $1 worth of wire, you have a tried and true method that works
great. The heat generated is distributed along the wire, just make sure
it isn't buried in a cable harness and the heat will disipiate without
any issues. Mounting a variac, even in a floor console Henry, jis not
without some mechanical complexity compared to this simple method, in my
opinion.
You definitely will benefit with a longer usable tube life with this
simple mod - voltages more than about 5% over spec apparently reduces
filament life significantly. Truth be known, we usually kill our tubes
in other ways compared to running them 10,000 hours with excessive
filament voltage, but that's another story!
73 Kevin K7ZS
MIKE DURKIN wrote:
> Ok.. yea i did search some on reducing the voltage at the heaters on google
> ... yikes alot of what in not really looking for.So a quick question .. what
> is the favored way to reduce the voltage ?? i have 12V ac across 2@3-500z's
> and i want to drop it by -- say 1 volt.
> Trying to keep to the confines of what i have around .. some 12 and 10Ga
> solid magnet wire, some romex (120v stuff) and some 12ga hookup wire witch i
> dont think the insulation is rated for heat at all ....
> Or some other common junk drawer stuff that would do the trick ... the last
> thing i tried was a .27Ohm 10W cement resistor and that was too high of a
> resistance ( was a bit surprised but oh well i dont know the internal
> resistance if the filaments anyways)
> KC7NOA ... i think i even have some nichrome sitting round some where.....
>
>
>
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