Driving Z570m tubes

[Craig Garnett]

The ongoing project of mine is coming on nicely but I need some reassurance with the way I'm driving the Z570s.

There are two banks of 6 multiplexed tubes, from what I see from the datasheet these should run at 2ma static or up to 12ma as a 1 in 6 multiplex but that is using google to translate from the datasheet's German.

The problem is that even with a 1K anode resistor I can't quite get 8mA from a 170V supply.

The photo shows two tubes, the left is static at 2mA and the right is multiplexed at just under 8mA with a 1mS on time from a 170V supply and 1K anode resistor..

Is this ok or could I do it a better way?

Thanks

Craig

[gregebert]

My concern is that over time as the tubes age your HV supply voltage might be too low to ensure proper ionization. If it's not adjustable, you can boost it with a series DC supply such as a wall-wart transformer or a small isolated DCDC converter. Anything from +12 to +24 should work fine, and the current is pretty low (12mA).

Once you get the HV supply resolved, you will be able to get more current thru the tubes. BUT......you may want to stay with 8mA. From the photo, the tubes glow nicely. Tube wearout is an exponential function of current, so staying at the lower currents is better for longer lifetime. At some point, the current could be too low and you might see cathode poisoning, but that's reversible. My gut feeling is that 8mA of pulsed current should be fine.

So, are you using rectified AC-mains as your DC supply ? No worries, I've done that on several clocks and it can be done safely with proper circuit design.

[Craig Garnett]

Thanks  gregebert

My HT is a 12V module and is adjustable but the tube spec says 170V so I left it at that.

Are you saying that it's safe to increase the HT to get maybe 10mA?

Craig

[gregebert]

You can run nixie tubes at much higher voltages if you wish, it does no harm as long as you increase the series resistor to keep the current within spec. For example, my first nixie clock runs the B5092 tubes from a +340V supply, and I used a larger resistor (75K I think) to get the optimal 2.2mA current. Running at higher voltage gives you more design margin, but it does waste more energy as heat. Generally my HV supplies run between +200 and +220VDC; seems like every clock I make ends-up with a different power supply design. So far, I've designed and built nixie clocks with B5092, B6091, B7971, IN-18, and RZ568m tubes.

I would bump your supply up to +200V, and adjust the resistor to get 8mA of peak current (6:1 multiplexing). That will give plenty of voltage margin as the tubes age.  From the photo, 8mA looks nice. I recommend that you view your tube as you vary the supply voltage to get currents between 5mA and 12mA just so you can see the effect of current on brightness. You should see that once the tube is lit "normally", increasing the current doesn't make as much of a change visually.

I dont run my tubes multiplexed for a variety of reasons.

[Craig Garnett]

Thanks gregebert,

I'll have a play with the HT voltage and report back.

Craig

[Craig Garnett]

Increasing the HT gave me 10mA and looks pretty good but is this an issue in the photo?

It only occurs in the multiplexed tube.

Thanks

Craig

[Greg P]

How much current are you using in a directly driven tube?  I’ve had the same issue with the pins lighting up with as little as 1mA on the Z570M tubes.

[Craig Garnett]

The directly driven tube is just 2mA and that doesn't light the pins.

If I swap the tubes then it stays with the multiplexed tube.

[Greg P]

Interesting.  

[gregebert]

I'm speculating that in order to get the higher current for multiplexed operation, the increased voltage was enough to coax a bondwire into glowing. I have a few 5031 nixies that are so worn-out that only the bondwires glow.

[Craig Garnett]

So is it an issue towards tube life or nothing to worry about?

Craig