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Neon Nostalgia

When you have glass bulb with some electrodes inside, pump it vacuum and let just a little bit of neon gas in, you have a neon lamp. Put a sufficiently high voltage across the electrodes, and the gas inside will be ionized, a current starts to flow and the neon will glow in a red-orange color. There are several ways to build neon lamps. Neon signs are shaped long glass tubes. They need a high voltage to make the neon light over a large distance between the positive and negative electrode.
In smaller neon lamps, a different type of discharge is used. At a moderate voltage the neon gas will already light. This type of discharge is called glow discharge. The discharge area is a thin blanket in the area around the cathode (the negative electrode). The blanket will form holes if the current is lowered. If the current is too high, some ions will leave the cathode and the color of the light will change. Eventually this will damage the lamp.

Neon glow lamps can be used as indicator lights, displays and even as voltage stabilisers . This is because the working voltage is determined by the physical properties of the glow discharge, that can be determined by the designer of the tube. Some very intricate applications have been developed such as counter tubes where the ignited plasma is handed over from electrode to electrode like the stick in an estafette race.


Nixie tubes

From 1950 to 1970 Nixie-tubes were a common technique for displaying numerical data. Within a nixie tube, there are a number of cathodes (usually 10), shaped as numerals from thin metal wire. The stack of numerals is enclosed by a fine mesh of thin wire, which is the anode. Only one cathode is used at a time, the glow discharge around the cathode, will make the neon around that cathode light in the shape of a warm, velvety, red-orange digit.

The wire-numerals are placed in front of each other. When a nixie tube is displaying the contents of a running counter, you can see the digits jump to and fro. The dancing digits make the nixie tube a fascinating thing to look at.

On a separate page How To Drive Nixies, I'll discuss the principles for nixie driving circuits.

In December 1999, I caught the nixie fever. I found that a local electronics surplus shop in The Hague had some boards containing 12 nixies each, at a very nice price. I couldn't resist and bought two of them, one with multiplexing circuitry and the other just a bus board, handy to experiment with. After that, I started imagining what I could do with it.


Pandicon multi-digit nixies

Philips and some of their sub-brands fitted 8-14 nixie displays in a single tube. These so-called “Pandicon” displays were intended for multiplexed displays for calculators etc. They have a B17A base on both ends. One has all the anode connections, the other is connected to the cathodes. I have two different pandicons in my collection, an 8 digit ZM1200 and a 14-digit ZM1200.
Philips ZM1200 14-Digit Pandicon

Philips ZM1200 14-Digit Pandicon. Digit height is 10 mm.


Panaplex displays

  Sperry Beckman SP-351 Panaplex display.

Sperry Beckman SP-351 Panaplex display.

There is another way to build numeric displays using neon glow discharge. One can arrange a number of metal strips in a 7-segment arrangement. This flat configuration can easier be read from an angle than Nixie tubes. Though the digits are not as well formed as nixie digits, these flat 7-segment displays have the same pretty orange glow as Nixies.

Sperry corporation produced multi-digit 7-segment flat planar displays under their “Panaplex” brand name. I particularly remember them from some advanced pinball machines in my youth.

I found a Berkel scale from a grocery shop that used these Panaplex displays. My Nordmende DiVo 3362 Digital voltmeter and my Feedback FM610 frequency meter also have them.

Panaplex displays on a Berkel weight scale

Sperry Panaplex 7-segment displays on a Berkel scale.

Philips also produced flat 7-segment neon displays. These were sold under their “Pandicon” trade mark. I have some ZM1500 7-segment pandicons. I also have a Japanese calculator that has a similar 8-digit 7-segment flat neon display.
Planar 7-segment calculator display

The planar 7-segment display in my Royal Digital calculator.


Neon stabiliser tubes

The fact that the voltage across a neon glow lamp is rather stable, can be used to produce a reference voltage. There are neon stabiliser tubes for voltages from 70-150 V (the 150 V types would contain other gases than just neon, as can been seen by the different, purple color that for example a 150B2 emits).

My old high-voltage regulated power supply uses a very old Japanese neon stabiliser as a voltage reference.
The GM7635 valve voltmeter has a 4687 neon stabiliser to stabilise its power supply and minimise drift. The 4687 is particularly charming because of its spiral electrodes.

Vintage equipment

I have a few pieces of electronic equipment that use nixie tubes or other types of neon displays, such as calculators and weighing equipment: measuring instruments:

Nixie panel meters

Besides complete multimeters, I also have some of panel meters, actually half-products to be built into a switch panel or larger instrument.

My nixie clocks

I also have some nixie clocks. Two I built and one I was given. In this 21st century, they strongly remind me of the 20th century and specifically the 1950's and 1960's, the “space age” with its optimistic expectations of the way high technology would shape the future of mankind.

Copyright © 2000-2014 by Onno's E-page         published 2000-10-20, last updated 2015-05-03