Buying Used Soviet Nixie Tubes: A Simple Checklist

Used Soviet Nixie tubes are an affordable way to build or repair a clock. This guide covers the IN tubes we carry: how they differ, what to check before you buy, how to fit them, and what to do if one looks dim.

Good to know: used tubes can have uneven brightness, and they are not the best fit for replacing one tube in a clock full of new tubes.

The IN tubes at a glance

Some tubes show the digit through the rounded top of the glass. Others show it through the side. Some sit in a socket on pins, and others have long wire leads for soldering.

Tube	Digit height	Digit seen from	Connects with	Decimal point
IN-1	17 mm	top	pins, socket	none
IN-2	9 mm	top	pins, socket	none
IN-4	17 mm	top	pins, socket	none
IN-12A	18 mm	top	pins, socket	none
IN-12B	18 mm	top	pins, socket	comma
IN-14	18 mm	side	wire leads	two
IN-16	13 mm	side	wire leads	two
IN-17	9 mm	top	wire leads	none
IN-18	40 mm	side	pins, socket	none

Six used IN-1 Nixie tubes with brown bases — IN-1

Six used IN-4 Nixie tubes seen from the top, with the digits visible through the dome — IN-4

Six IN-12A Nixie tubes seen from the top, with the digits visible through the dome — IN-12

A used IN-14 Nixie tube with its wire leads — IN-14

Six IN-17 Nixie tubes with colored spacers and wire leads — IN-17

The IN-13 is a different kind of tube: a glowing bar used as a level meter, not a digit tube.

An IN-13 bargraph tube fully lit, lying next to a ruler

Before you buy

All digits work. A photo of one lit digit isn’t enough. Ask whether every digit, 0 to 9, was tested, plus the decimal points if you need them.
Pins and leads look healthy. Look for bent pins, cracks near the glass and old solder.
Wire leads are long enough. New IN-14s and IN-16s have 35 mm leads. Used ones may have been cut shorter, so make sure they will reach your board.
IN-12A or IN-12B. Only the IN-12B has the comma. A lot sold as “IN-12A or IN-12B” can contain either.
IN-4 version. IN-4s were made with one anode or two, and the pin connections differ. Check which one your clock expects.
Sockets and spacers. Check what’s included and whether it fits your clock.
Replacing one tube? In a clock with new tubes, use a new (NOS) tube; a used one may not match them. In a clock with used tubes, ask for one with similar brightness.

Twelve used IN-12 tubes with black and brown sockets

Why a tested tube can look dim in your clock

We test each used tube before it ships. For used IN-18s, our test supply has been 200 V or more. Even so, used tubes can differ in brightness from one tube to the next.

Clocks don’t all drive their tubes the same way. When buyers have told us a tube looked dim, the clock sometimes ran at a lower voltage than our test setup. With less voltage or current, a tube can glow dimmer or unevenly.

Most of these tubes’ factory sheets ask for a supply of at least 200 V (the IN-16’s sheet says 190 V). The current per digit depends on the tube: the IN-18, for example, needs 4–7 mA.

If your tubes look dim:

Compare them at the same brightness setting. Night and dimming modes make tubes look darker.
Check your clock’s high-voltage setting against the tube’s factory sheet.
Don’t just turn the voltage up. Check the clock’s manual first. Its parts and current limiting have limits too.

Fitting the tubes

Safety first: unplug the clock and let its high-voltage capacitors discharge before you touch the tubes.

Tubes on pins: IN-1, IN-2, IN-4, IN-12, IN-18

Line the pins up with the socket before you push. Don’t use the socket to straighten a bent pin.
Turn the socket so the digits stand upright. The IN-1 and IN-2 factory sheets show which way it should face.
IN-12: The type is printed on the glass, so you can tell an IN-12A from an IN-12B. Some used IN-12s have old solder on the pins; they should still go into the socket without force. If you solder straight to the pins, stay at least 4 mm away from the glass.

Used IN-12A and IN-12B tubes side by side, with the type printed on the glass

IN-18: The base has a small glass tip in the middle, so make sure your socket or board leaves room for it.

Base of an IN-18 tube showing the ring of pins and the glass tip in the middle

Tubes with wire leads: IN-14, IN-16, IN-17

Set the height and line the tube up first. Trim and solder the leads after that.
IN-17: The leads are numbered from one deliberately shorter lead. If all the leads on a used IN-17 have been trimmed to the same length, check the orientation carefully before soldering.

Six used IN-14 tubes with spacers, with leads of different lengths

After fitting

Run through 0–9 on every tube, at normal brightness and at your night setting.

The IN-1 and IN-2 factory sheets recommend switching between digits regularly. If your clock has a mode that cycles through all the digits, use it.

If a digit looks wrong and your clock has sockets, swap two tubes of the same type:

The problem moves with the tube: it’s the tube or its pins.
The problem stays in the same spot: it’s the socket or the clock.

Still not right?

Send us the tube and clock model, a photo or short video, and your brightness setting. If you know the supply voltage or tube current, add that too.

Our test shows a tube worked in our setup. It can’t promise identical brightness in every clock, but a digit that won’t light fully is worth telling us about.