IN-13 Current question

[Bill Esposito]

Hey everyone -- It's been a long time since I've posted to this group (or played with Nixies for that matter).

I've built an IN-13 driver circuit, using a topology that seems to be the "canonical" one most commonly floating around the web, using an opamp and an MPSA42 -- see the linked schematic:

http://puu.sh/iNgTq/3f60ecf956.jpg

All values are measured full scale indication conditions. I'm using a Taylor Edge supply module set at 146V (as indicated on the schematic; I know my handwritten 4s looks like 9s to some people). I originally had it set at 140V, but one of my tubes wasn't reliably striking at 140V, so I changed the set resistance.

Thing is, all the documents on the IN13 that I've seen indicate that the control current should be on the order of 0-5mA. With the tubes I've got on hand (I've tried this on 3) the control current required has been on the order of 13mA to get the bargraph to indicate full scale.

The question is, why to I need 3x the rated current to get full scale? It seems like I MUST be doing something wrong, but I'm not seeing what it could be. I suspect this isn't good for the tubes long term, but I'm also not sure how bad it is.

As an aside, I tried 392k resistors on the cathodes and those gave me a slightly less linear sweep but overshoots the full scale indication slightly, which is nice. If there's no long term harm in upping that resistance, I'll probably go back to the 392k resistors.

Thanks!

-Bill

[Nicholas Stock]

Bill, I'm by no means an expert on this, but from what I've gleaned with the IN-13 tubes is that they sometimes need a little bit of over current to get them 'settled/conditioned'..after which you can use them full scale according to specs..try burning one in for a while then reducing the current and seeing what happens...

Cheers,

Nick

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[Bill Esposito]

Thanks for the thoughts, Nick. I haven't done long term burn in constantly at full scale, which I will give a try. I have given these tubes around 12-18 hours of use in a VU-Meter circuit, which has been pretty reliably bouncing up to 80% scale regularly and I haven't seen a change in bias current.

To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/CAOX%2BRHL-5%3D%3DEDfeVemBe7b2N%3DoTDR1-aFnqQLhRQ42hZ%2BzdimA%40mail.gmail.com.