09-07-2014, 01:46 AM
One thing that must be said though is that a wire wound resistor has some safety factor to it, other then getting as hot as a poker. When a wire wound resistor fails it normally goes open, much like a fuse. With the capacitive dropper and the diode dropper there is the possibility that it could short out putting full line voltage across the filament string if you don't take that into account.
Thankfully you can find large value non polarized capacitors that will fail open rather then shorted, I've seen them on the Mouser site, and in the case of the diode you can chain two together in series. In the case of a diode dropper, don't use a 1N4007, those are current rated only for 1 amp, use diodes rated for at least 3 amps. The tube filaments in these early sets are normally 300 ma or 1/3 of an amp which sounds like lots of head room but why cheapen out? 3 amp diodes are still much cheaper then new tubes, even in pairs.
Regards
Arran
Thankfully you can find large value non polarized capacitors that will fail open rather then shorted, I've seen them on the Mouser site, and in the case of the diode you can chain two together in series. In the case of a diode dropper, don't use a 1N4007, those are current rated only for 1 amp, use diodes rated for at least 3 amps. The tube filaments in these early sets are normally 300 ma or 1/3 of an amp which sounds like lots of head room but why cheapen out? 3 amp diodes are still much cheaper then new tubes, even in pairs.
Regards
Arran
