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This clock features a single Russian IN-18 vintage nixie tube

The entire clock, including its power supply, fits into a small bevelled acrylic cube which I machined for the purpose. The cube is sprayed in a metallic pewter colour. The top of the cube is drilled to contain socket pins for the tube, which were originally intended for use in a female ‘D’ socket.

I am rather fond of single tube clocks. It makes the best use of a vintage nixie tube and exercises all the cathodes.

To tell the time, the clock runs through the sequence of tens of hours, hours, tens of minutes and minutes before pausing and repeating the cycle. It is surprisingly readable.

The Russian IN-18 tube was one of the largest tubes available in quantity at accessible prices, but in the last few years prices have soared. Used or substandard tubes have also surfaced. Sources of these tubes are either drying up or the Russians are deliberately maintaining an artifical scarcity in order to keep prices high. Personally I believe stocks are finally drying up. Demand remains high for these tubes.

Peculiar pinout

As I was to discover, the geometry for the pins is very strange. The pins are on an 18mm circle at 24.5 degree intervals, which do not divide up equally into a full 360 degree circle, nor are any of the pins square on to the front, back, left or right sides. I drilled a trial socket in a piece of acrylic and when I was happy I used it as a template to drill my cube.

A ‘Polymorph’ nixie tube socket

As a later exercise I thought I would see if I could make a suitable socket out of ‘Polymorph’, a substance that will melt in a cup of hot water to a waxy consistency, but which sets to a really tough nylon consistency at normal temperatures.

‘Polymorph’ is purchased as small granules which can be reused as many times as desired to make all kinds of things.

I found the plastic middle from an old adhesive tape roll, cut some pins to go in the holes in my template, glued the roll middle around the pins and squidged some ‘Polymorph’ into it. It worked very well.

I pulled the temporary pins out and fitted the socket pins instead, which were a comfortable friction fit.

If I needed mounting flanges I could melt some more ‘Polymorph’ and it will adhere perfectly to the sides of the socket I have made.

All in all I’d say this is a good solution if you cannot find a suitable socket for sale.

The electronics

The picture below shows the disassembled clock.

A small piece of veroboard holds the PIC and driver transistors, with a mains power supply attached at right angles to it. Two switches allow the time to be set through holes in the back of the case. This is a very minimal circuit design.

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