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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?

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  • \$\begingroup\$ I've got a flashlight that flashes at 96 Hz, and it's totally obvious to me. Move the light or sweep your eye from side to side and you can see flickering easily. It's like a biological oscilloscope. \$\endgroup\$
    – endolith
    May 13, 2011 at 19:32
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    \$\begingroup\$ @endolith - i know what you mean, i can see the flickering in the LED tail lights on certain cars. but in the case of nixie equipment, it's usually the viewers head moving, not the display. stroboscopic effects seem worse when its the display that moves. \$\endgroup\$
    – JustJeff
    May 14, 2011 at 13:35

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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:

  • It's cheap. For $1.25, you can have decent regulation of your supply voltage. I'm assuming the isolation transformer is already accounted for.
  • You can/will see the nixie tubes flicker at 60 Hz.

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.

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  • \$\begingroup\$ Well written, I would like to note, something with a high turn on voltage is normally visible when the on AC wave only lightly passes it as it spends a significant amount of time off at 60Hz and your eye will see it. \$\endgroup\$
    – Kortuk
    May 16, 2010 at 5:56
  • \$\begingroup\$ I have a voltmeter which uses 60Hz Nixie-tube flicker to avoid the need for latching circuits. During one half of each line cycle, the display shows a reading; during the other half, a new reading is acquired. I certainly haven't found the 60Hz flicker objectionable. \$\endgroup\$
    – supercat
    Mar 13, 2011 at 18:13
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    \$\begingroup\$ @supercat To each his/her own. I notice flickering, and it bothers me. I don't like the LED car tail lights that are pulsed either. Making the display not flicker is a (usually low) price I'm willing to pay. \$\endgroup\$
    – W5VO
    Mar 13, 2011 at 18:42
  • \$\begingroup\$ I suppose if there's no reason to have the displays flicker, it would be advantageous to have a regulated supply (how noticeable would 120Hz flicker be, btw?) In the case of the meter I have, the flicker is there for a reason. Of course, if one is multiplexing a display, it may be necessary to have a filter cap on the supply to ensure all rows or digits are uniformly lit (sometimes I see display that look like they're being scanned rather slowly; I suspect the real scan rate is close to 60Hz or 120Hz, a filter cap failed, and I'm seeing a beat frequency). \$\endgroup\$
    – supercat
    Mar 13, 2011 at 19:08
  • \$\begingroup\$ Another reason to consider something other than the OP's idea is safety. Maybe you're not comfortable running 115VAC, 10A, into your homemade clock. I wasn't, so I used a 6VAC wall wart run into a step-up transformer. \$\endgroup\$
    – John Lopez
    May 13, 2011 at 3:30

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