I've seen any number of nixie tube designs on the web that use regulated 170V supplies for the nixie tube anode.
Wouldn't it be possible to use unregulated, half-wave rectified 170V peak power for this? Yes, the illumination wouldn't be continuous, it would in fact flicker at 60Hz, but this is fast enough that it shouldn't matter to the human eye. The brightness would vary with line voltage, but since that doesn't usually vary more than a couple of percent, this effect also should go unnoticed to the casual observer.
The up-side of this would be that you could dispense with the relatively costly regulated supply, and use a simple 1:1 isolation transformer and a single rectifier diode to get the anode supply, since sqrt(2) * 120 gives very close to 170.
In fact, if you used SCR's to pull the cathodes to ground, you could do away with the rectifier, because when the AC reverses direction, the SCR will cut off just like a diode. A single current limiting resistor should suffice if placed on the anode side of the tube.
Would it work? If not, why not?
Best Answer
Sure, it would work.
I have used a slight step-up transformer (120v to 130v) to drive a nixie supply. It also had a 6.3v filament tap which was really convenient for the 5v ttl logic supply. However, I used a full-bridge rectifier followed by a electrolytic capacitor to filter both supplies. Here's why I would recommend that setup over what you're suggesting:
The motivation for fancier regulation circuits is to protect the nixie tubes. They are usually the focal point of any design using them, so it's in the designer's best interest to make sure nothing bad happens to the tubes. I've seen people drive nixie tubes with expensive regulated bench supplies, and read about people using unisolated circuits. Somewhere in that range is a cost-benefit-paranoia tradeoff.