IN-8-2. 170v supply, direct drive. What anode resistor?

[celzey11]

Seen a lot of discrepancies for what people recommend for an anode resistor. I want to prolong the tube life as long as possible as it's going in a full custom clock that's gonna be a gift.

[Kevin A.]

I would recommend a value around 18k for 170 volts. That's what I run in my clock that has IN-8 seconds tubes. 

Of course, if tube life is a concern then I would also add in a motion sensor and a phototransisitor to automatically dim the tubes in low light. These two things will help any nixie live a lot longer than a few percent difference in the anode resistor. 

On Fri, Jul 17, 2020, 7:25 AM celzey11 <celz...@gmail.com> wrote:

Seen a lot of discrepancies for what people recommend for an anode resistor. I want to prolong the tube life as long as possible as it's going in a full custom clock that's gonna be a gift.

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[gregebert]

The datasheet I found online says the operating voltage is 100V, and 2.5 to 4.5mA. So I would start with the midpoint, 3.5mA

If your supply is 170V, and the tube is 100V, the resistor is easily calculated:  R = (170-100)/(0.0035) = 20K

I'm very suspicious about the 100V operating voltage; it seems too low for me. But I've never experimented with IN-8 tubes, so maybe it's correct. Most tubes I've used operate around 140V or higher.

Best thing to do is measure the voltage across several IN-8 tubes when it's drawing 3.5mA, average the result, and recalculate the resistor value from that.