Lighting up NIXIES after many decades - Page 1
Forum section: electronics / projects

author: ppTRN
author_rank: Regular Contributor
timestamp: August 03, 2023, 01:25:17 pm
content: Hi,I came in possession of some NL-841 Nixie tubes and I am developing a circuit to make them work. Digit selection will happen via a 74LS141. To generate the anode voltage I think I'll use a 230V to 12V transformer and a NE555 oscillator to generate a 13V square wave to feed to the 12V side of the transformer and getting 250V on the 230V side.Now the main question: since the tubes have not been used for a really long time, should I follow some dedicated procedure to avoid brutally killing them? Should I start with a smaller voltage (For that I may use a variac)?Thank you.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 03, 2023, 03:24:02 pm
content: Quote from: ppTRN on August 03, 2023, 01:25:17 pmNever heard of that, where from did you have such info? Why would that be useful for a Nixie tube?The only slow start/variac trick is to reformat very old electrolitic capacitors. In time the oxide layer of the capacitors dissolves in the electrolyte, and applying a voltage slowly increasing over many hours will regrow the oxide layer inside the capacitors. Has nothing to do with tubes or Nixie's.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: August 03, 2023, 03:27:48 pm
content: Hi ppTRN,don't run them in multiplex-mode,the high peak-currents might kill them.Good luck

author: ppTRN
author_rank: Regular Contributor
timestamp: August 03, 2023, 04:17:02 pm
content: Thank you for the replies. By multiplex mode do you mean also switching on and off the plate voltage? I was not planning to do It. I would leave all plate tò HV and use the decoder tò ground the digit i want tò light up

author: Gyro
author_rank: Super Contributor
timestamp: August 03, 2023, 06:46:58 pm
content: Running them in non-multiplex mode (as you are planning) ensures that the cathode (digit) currents are low and steady, if multiplexing a 4 digit display you would run the cathodes at 4 times the current for 1/4 of the time to achieve the same average current spec.Don't forget the Anode or Cathode resistors, even for a moment. Run the displays as close to the specified minimum current as possible, this will increase their lifespan and still be plenty bright enough. Note the recommendation in the datasheet about using individual cathode resistors rather than anode resistors if you are using the (much lower current) decimal point.Running at higher supply voltage with higher value current limiting resistors is best, at least initially. Old displays might have trouble lighting (at all or evenly) at the minimum 170V spec. Higher supply voltage (within spec) and correspondingly higher resistor values makes it easier to control the cathode currents too (easing the demand on supply voltage regulation). At the minimum 170V spec, regulation and resistor value become critical, with a small change causing a large change in cathode current.TheMOSTimportant rule is not to leave a single cathode illuminated for extended periods. This can cause poisoning of the non-illuminated cathodes, eventually causing uneven illumination and dark spots when they are turned on. This is more of a problem at high cathode currents but always cycle the digits.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: August 04, 2023, 12:46:13 am
content: Yes, don't forget the current limiting resistor(s).You may find that the digit wires may not completely glow showing incompletly formed digits. But they will heal in time. Personal experience using some tubes idle for 35 years. This project:https://hackaday.io/project/183352-repurposing-an-old-nixie-thermometerBTW.