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Registered Member #122
Joined: Fri Feb 10 2006, 12:55PM
Location: Milano Italy
Posts: 148
I wouldn't do that, because when you turn it on just at the "right" time, the filament can get the full peak voltage across it (330V), it'll "tick" and the fun is over.
Isn't true! The resistance of a cold filament is much lower than a fully heated one. if you use a regular transformer the filament will suffer an high inrush current at every powerup, at the contrary, the capacitive reactance of the capacitor remains the same and is many times bigger than the resistance of the filament (hot or cold)
when you power up the filament with a capacitive divider the voltage across the filament slowly ramp up following the resistance (and hence, the temperature!), the filament of my plasma lighter reach the fully operational temperature in about two times the time required for the same tube powered via a transformer.
trust me, the capacitive divider is a great solution, of course you need some extra attentions during the wiring to avoid excessive voltages between the filament and the catode (the oxide layer is quite thin), expecially if both filament and plate are directly powered by mains voltage!
Registered Member #286
Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399
I have made a very small VTTC using a 6BQ6GTB. The filament was powered by a homemade SMPS. A capacitive ballast may work. I have never tried it. Good luck.
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Vacuum tubes with 117v filaments for VTTC
