In my reading about linear amplifier design and construction I have noticed in a couple of writings that if the filament voltage on say, a 3-500Z tube, is reduced from the typical 5.0 VAC to around 4.8 or 4.9 volts, tube life can beextended several fold.
In an article by AG6K on QSK for the TL-922 and SB-220 he mentions that
a good method of reducing the filament voltage (at the socket) is by
using smaller guage wire from the transformer to the socket. He mentions that
it should have good (teflon) insulation. My question is: Is this really the
best way to reduce the voltage? Seems like varying line voltage would necessatate using some sort of rheostat? Any ingenious methods out there? I am planning onusing a step-start relay to initially start the filament voltage low to reduce
inrush current on a 4-1000 tube.
I have already implemented his method of biasing the tubes by putting
a string of diodes in the cathode return line. This is in place of using a
high wattage zener. This works fine, as you can fine tune the idle current on
