Don’t you just love nixie tubes? They glow with a lovely neon color and have gorgeous stylized numbers– something you can’t get with a dot matrix– or even sixteen-segment LED or LCD display.
From the 1950’s until about 1970, nixies were a dominant display technology. “NIXIE” is actually a brand name for display tubes made by Burroughs, and the proper generic name might be “cold cathode neon readout tube.” However, as with facial tissue, a single short word involving the letter ‘X’ had more widespread appeal. Whatever you call it, they were used in all manner of electronic instruments that needed to display numerical data until they were ultimately made obsolete by the introduction of LEDs. One of the common places that you can find nixie tubes is in old scientific instruments, like this old HP 5321B frequency counter which has been converted into a clock. (It’s 10:53:49 PM.)
The tube that we’re taking apart is the kind found in the clock (counter) shown above. It’s a medium-size, upside-down vertical, side view, medium digit nixie tube with a neat rounded bottom– or top, depending on how you look at it. The HP part number is 1970-0025, equivalent to Burroughs B-5560 and National NL-918. You can get tubes of this type from Sphere for $10 each.
The ideal tool for getting at the insides of the tube would be a lathe. We didn’t have one handy and so we had to improvise. The tube turned out to fit into the keyless chuck of our drill press, so we directly (and gently) clamped it in the chuck. With the drill press set to its lowest speed, 300 RPM, we held a fine-edged diamond file against the base of the glass tube.
This worked very well. After a couple of minutes, the scoring from the file turned into a neat cut, and the top of the tube fell right out onto the rag we placed strategically on the platform.
It was a fairly clean break, but the top of the tube cracked in the drill chuck, probably after the tube bottom was removed.
Next, the mica insulator at the top of the tube (bottom of the digits) was removed. The screen around the tube was held on by several tack welds. You can start to see the individual numbers here, from the side.
The individual numbers are held apart by ceramic spacer beads. Notice that there is an extra eight, but upside down. It is the one with the wire sticking out. That one was used as a wire, and did not light up.
Here is the real reason for taking apart the tube: the beautiful numbers. The four is out in front, which makes it seem brighter. When in use, you can tell what number is lit by placement almost as much as by shape.
Each of the numbers is connected through a ribbon-shaped wire to a pin on the base. Fortunately, these can be cut with fine-point scissors.
Just a few more pieces to go. With the metal screens removed, you can see the remaining characters much more clearly.
The set of numbers is beautiful. Notice that there are two identical 8’s, and that the “one” is made of two lines. This helped to keep it as bright as the other numbers in spite of being so much smaller.
We hope you’ve enjoyed this as much as we did. We’re already plotting what to take apart next…