[Amps] How best to reduce filament voltage?

[David Lisney]

Hi, depending on the construction of your mains transformer sometimes it is 
feasible to slip a few turns of ordinary connecting wire round the bobbin as 
a "buck" winding. Obviously you will need to select wire of adequate current 
rating. A friend has a commercial 4CX350 style amp, in the past someone had 
done a creative bodge to make it run with the B version with it's 6v heater. 
The thing was a mess with a small transformer hanging out of the back of the 
amplifier. In this case 22 turns of wire round the bobbin of the original 
mains transformer sorted us out. Obviously in our case we only needed 2 amps 
so could use very small conductor but maybe worth a thought in your case. It 
maybe worth checking your voltage at the socket itself, at the current you 
are dealing with it maybe significantly lower at the valve base.

To drop that half volt you may need less than 2 turns of "bucking" wiring in 
antiphase to the original filament supply... just an idea.... maybe easier 
than finding a spot for a small wirewound.... Regards David G0FVT