IN-14 and Mystery Tube?

[Derek]

Hi guys! A few weeks ago I ordered a set of IN-14s off of ebay. I wanted to ask a couple things about them.

First off, I got six of them for $25, free shipping from Ukraine. Was that a good deal?

Second, is there any way to get a rough estimate on how much "use" they have seen? I'm looking at them, and they seem almost brand new. Seller says he ripped them out of a calculator, and doesn't know how much they were used. As far as I can tell, all the markings are in perfect condition, and all the digits are still shiny and whatnot.

Third, it turns out that the seller also included four extra tubes. I don't know the model, but it looks like they are INS-1s. Is my presumption correct?

[Roddy Scott]

You are correct in thinking that they are INS-1 neons. Your seller would have thrown these in as a freebie as they are about 50 cents each.

Telling how much usage a tube has been subject to is not easy. Quite often if they have been taken from working equipment they could have been used quite a bit. From a calculator you could expect them to have been busy for their time in it. One check that can be made without power is to take a look at the condition of the cathodes, in excessively used tubes cathodes will be grey looking while lightly used ones will be more metallic looking. The tube in your photograph looks to have been used quite lightly or not at all and could have been pulled from a calculator that was not used. Only when they are powered up can you see if there are any issues with the display. The only drawback of recovered nixies is the way in which they were removed. Excessive heat applied to the connections to the circuit board they were removed from could affect the seal around the wire from the internals in which case they could lose the gas from the envelope. Looking again at your photo, your tubes look to have been mounted with stand offs which reduce this risk on removal if it is done carefully as well as perform their task of supporting the tube safely when in position.

Some of the contributors here have had IN-14 nixies running in clocks for years without any issues.

Value wise, $25 for 6 second hand tubes is OK as NOS run around $40 to $60 for 6 depending on the seller with some bargains such as $40 for 8 (ex shipping) making them $5 a tube. If you are buying IN-14 nixies in the future it pays to go for NOS with the full lead out wire length then you will know that they are more likely to last longer but as said, they can run for a long time with no issues.

Good luck with your clock project.

[Derek]

Thanks! It looks like the leads were clipped, so I believe no desoldering was done. The cathodes look extremely shiny/polished, so my hunch is that this calculator just sat in some Ukrainian basement collecting dust, maybe used every once in a while. 

Another question, I bought a six pack of russian 74141s, but haven't had a chance to test them out. Is it safe to drive these chip inputs directly from an Arduino pin, or through 74HC595s? I understand that these chips have zener diodes built in, among other things, but could a faulty chip totally destroy my arduino? I'd rather prevent magic smoke.

[gregebert]

If everything is properly connected, even an internal short in the 74141 that leaked high-voltage back to the Arduino, which seems unlikely, would be limited to a few mA so it's unlikely to cause damage.

Your biggest risk is a hookup error, or possibly ESD damage to the Arduino from mishandling.

[Paul Andrews]

Tell me about it :-/ I had smoke coming out of something the other day. Amazingly nothing was damaged. Live and learn!

[Terry S]

Seems unlikely. If it smoked, you did damage. Nothing in the semi world gets hot enough to cause smoke without some damage. 

Revisit your circuit. If it hasn't failed yet, it will.

Terry

[judg...@gmail.com]

It wasn’t the circuit. And just bread-boarding stuff, so if something breaks it gets junked!

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[JohnK]

You run another risk.. the thing that smoked might have changed its characteristics compared to a 'new' one. Can make a mess of cut-and-try design.

 

John K

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[Derek]

Sweet, thanks guys! I plan on putting the high-voltage portion of the circuit on a separate breadboard to keep things on the "safe" side. I'm pretty anal about making sure my connections are correct before I power any circuit up.

Paul, are you sure it wasn't a resistor, diode, or even a cap? Our class worked on a power supply project last month, and the most common cause of magic smoke that I've seen was because somebody dumped too much current into a diode, or screwed up the polarity of their capacitor. The diodes sheared right in half....

[Paul Andrews]

The only components in there were resistors and the breadboard itself. Voltages were nixie level. I would say it was either a resistor or the breadboard itself. I am pretty religious about measuring stuff before I turn the power on (and after), and if there had been anything more complicated in the circuit I would have tested it separately afterwards. 

Anyway, I only mention it to point out that you can't be too careful but even so, things can go wrong. It is all a learning experience!

On Mar 13, 2017, at 2:22 PM, Derek <imchil...@gmail.com> wrote:

Sweet, thanks guys! I plan on putting the high-voltage portion of the circuit on a separate breadboard to keep things on the "safe" side. I'm pretty anal about making sure my connections are correct before I power any circuit up.

Paul, are you sure it wasn't a resistor, diode, or even a cap? Our class worked on a power supply project last month, and the most common cause of magic smoke that I've seen was because somebody dumped too much current into a diode, or screwed up the polarity of their capacitor. The diodes sheared right in half....

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[gregebert]

I no longer breadboard projects, because PC boards are so inexpensive and their quality/neatness far exceeds anything I could do on a perfboard. I recently did a small HV supply for nixies; for $21 US I got 3 high-quality PCBs from OSH Park. They charge $5 US per square-inch, which is great for small boards.

A PCB is much more compact than a breadboard, and it allows you to use surface-mount parts which are not only smaller, but also cheaper, than thru-hole devices. While it does take time to do a PCB layout, keep in mind that it takes a great deal of time to manually wire-up each component on a breadboard. Wiring errors, shorts, and open are much less likely on a PCB. Also, having the schematics captured for PCB layout will get you a netlist you can simulate (ie, SPICE), which means you can greatly reduce the amount of experimenting & debugging.

 All-in-all, I think I spend less time designing+simulating+building+debugging a PCB than a breadboard. Where the big savings come-in is when you need 2 or more boards.