T.
Does your set use a series string or a parallel 6.3 volt circuit? If it is of the parallel type, you can build a voltage doubler, and then put a resistor in series with it to boost the voltage a little (7 or 8 volts...you don't want 12.6 volts). You can also use a center tapped secondary of the medium size 12.6 volt transformer that Radio Shack sells (if you have a parallel filament circuit). Wire one half of the secondary to the filament circuit. Wire the entire secondary to the picture tube filament through an appropriate resistor. Most 6.3 volt picture tubes draw 600 mA, so it should be fairly easy to do the math for dropping 12.6 volts to 7 or 8 volts.
I have a parallel type brightner, but I really don't want to part with it.
Thomas