Auxiliary Dekatron Stuff

Extra Stuff

(Click on Drawings to Enlarge)

Quick Pinout Guide of most Common Dekatrons:


A101 Alignment:

Front, or top view, as looking from the top of the tube. K0-K9, on the inside orange disk is the physical location of those 10 main cathodes, where the glow will reside. The numbers on the outside of the orange disk, is the pinout, as viewed from the top. Pinout chart on the side shows electrical pin assignments. Example: Pin 12 aligns physically with K1, though K1 is electrically tied to pin 13.

3-Guide Dekatrons:



More often referred to as Single-Pulse Dekatrons. These were the first version of high-speed dekatrons. High speed meaning ~20KHz to 30KHz, as opposed to later high speed types, that went as high as 100KHz (2-guide), and 1MHz (1-guide). Standard speed being around 5KHz. The 3rd guide, meant that these tubes had 40 cathode rods, instead of 30.

Above is the original intended drive circuit for this type (single pulse) of dekatron. Issuing a negative going pulse, goes to guides G1 & G2. G1 has an RC (differentiator) pair in the path, which speeds up the pulse, so the glow transfers here first. Just a few microseconds later, the glow is shared with G2. Upon the end of the pulse (it rising), G1 again will get there first, so G2 now has the pulse all to itself. A few microseconds later, it too will go positive. The glow, now will transfer to the closest cathode, that is more negative. That will be G3, which is sitting at ground (0V) level. G3 is tied to Gnd, thru an RC pair, too. Once it gets the glow, its also starts conducting. This will cause the voltage across that RC to rise, also raising G3. At some time later, that voltage will be high enough, so the glow will finally transfer and rest at the next main cathode.

This is quite a different drive circuit from the standard 2-guide (double pulse) dekatron. Of course, with modern circuitry, we can just ignore using this type of circuit, especially using something μC driven.

Typical Drive Spec:

Above is the nominal range that a typical 2-guide neon filled dekatron can operate within.

Mini Dekatron Photos:

The dekatrons above are all roughly the size of a 6J6 (ECC91) vacuum tube. The GC10/2P, was the first of this size, and the 6879 was a close second source. Both are 2-guide standard speed dekatrons, though due to the size, they are only to be operated upto 1KHz. The ZM1000 is a nixie, not a dekatron, and only included as a size reference. The EZ10B is a single guide dekatron, which uses the guide shape, in place of two guide sets, to route the glow direction; clock-wise only. That, and the gas mix of hydrogen, instead of neon, allows this tube to clock at close to 1MHz. The fastest dekatron ever made. Unfortunately, by the late 60’s, a semiconductor IC counter, like the 7490, could count at close to 30MHz, and only require a 5V supply. Plus by 1970, a TTL counter cost less than a dollar, while dekatrons still cost more than $10. Doesn’t take a rocket scientist to see which technology would prevail.

Here are more miniature types, that came to market, by the 60’s. The fatter ones are close to the size of compactrons (a GE form factor). Compactrons, however, have twelve pins while these mostly have 13 pins. The GS10H has 17, and the WE 6167 has 19. Most of these tubes have sockets that are damn near impossible to get nowadays. Only the GC10/2P (the skinny one of bunch) uses a common 7-pin mini glass tube socket.

More Spinner Circuits:

Power directly from AC line (either 120 or 220VAC) that generate voltages needed for most dekatron projects:


Note: that the voltage appears to be tripled for the 120V (110V, 115V, 117V) circuit, though it looks like a common doubler. It IS a doubler. The magic is in the source voltage. The 120VAC, is actually a 330Vpp wave. Its the Peak-to-Peak value that gets doubled. But here its 330V added on top of the 165V half wave rectified. 165V is the peak value of a 120Vrms.

In the 230V circuit, its only doubled, but a half wave rectified voltage is also provided. in the 230V circuit, we are adding nothing on top of the 660Vpp wave. Only offseting it up 330V. Note, the red voltages, by D2, in both circuits.

If you want to run some low voltage circuits, in addition to those used above, here is a add-on, with the line frequency clock source, too:



Neon Relaxation Oscillator Variable Speed Dekatron Spinner powered directly from AC line (above). Uses either the 115VAC or 230VAC power supply, two drawings up. The anode resistor, Ra, is required. For 115VAC use the 680K shown. For the 230VAC supply, Ra, is part of the supply circuit, in the form of the 2 1.2Meg resistors, RA1 and RA2.

Relax Osc Spinner, using a 0A5 Gas Trigger (above).

Variable Speed Spinner using a 556 (Dual 555) as both HV voltage switcher (from Low V) and pulse generator to spin dekatron. (above)

Similar to 556 circuit, but uses a LM393 Dual comparator chip instead.

Neon Relax Osc Spinner, showing different values for varying supply voltages. (above)

Combine the LM393 based supply with Relax Osc spinner, and get the circuit below (click to enlarge):

Adapted to run a very picky Western Electric WE-6167 (click on image to enlarge):

A Dekatron Pendulum using discrete components. No ICs (click on image to enlarge) :


Another supply option:

Tube based power supply, for running dekatron spinner circuits.

Below, is a circuit showing how to drive a dekatron with a GTE175M gas trigger. This trigger was specially designed for dekatrons. It can take the 20V pulse from a dekatron, and boost it to over 120V, in order to pulse a successive dekatron.

Basics for operating an A108 mini Russian dekatron:


The A108 is a special unidirectional dekatron, that has no unique guides. The odd or even cathode groups can be used as guides, making this a divide-by-five tube, instead of a true dekatron. The drawing below shows the basic pinout, and a couple of different spinner circuits (click on drawing to enlarge):


Note how the cathodes are in two groups, KE & KO. In the first circuit, one group, is tied to a simple RC network, while the other group is commutated (pulsed). For more uniform stepping, an astable multivibrator, with complimentary outputs is used.

Below, is a link to a video, showing the uniform stepping, of this tube:

A108 Spinner Video

Here’s a simple 555 based spinner:


From some more experimenting, I found that the A108 will work with anode supply as low as 250V. Maybe even lower. The 555 circuit shown, has a duty cycle very close to 50%, and the glow is uniformly share between the odd and even cathodes. The cathode resistor, on KO can be as low as 4.7K, but not all the way down to zero. This circuit has a 20:1 speed adjustment range.

Revisted & dolled up the simple spinner:

(click on photo to view video):



Since the A108 can run at voltages just a tad over 200V, I decided to incorporate the cheap “Fet-less” power supply, into the circuit:


(click on, above, to enlarge drawing):

The A108 cathodes must serve as both guides (inputs), and mains (outputs). To do this, isolating circuitry needs to be added. Here is a demo circuit (click on drawing to enlarge):


The two complimentary pulse groups, KE & KO are isolated from the cathodes, with BAV21 diodes. The pulse sources, are normally biased up at ~+25V. This keeps the diodes in reverse bias, so the pulse sources are effectively isolated. The complimentary, pulse sources, also go thru capacitor differentiator, which make narrow pulses, that are biased, so that they will go below zero (negative). When less that zero, the diodes will be in forward bias, and drag on set of the cathodes down, causing the glow to transfer. Since its only a narrow pulse, the cathodes, will resume their ouptut function, in short order. In a real usable circuit, those outputs will be the BE junctions of NPN transistors. In this demo circuit, the BE junctions, are LEDs.

Click here to watch video, of the circuit in action.


A107 Dekatron

The A107, is similar to the A108, but it barely glows a dim purple. It needs 500V versus 300V for the 108. And at that 500V, it needs to draw 1.5mA. Also, I use stepping pulses of ~120V, biased so that it rests at +60V, and steps down to -60V.


Click here to see a video of it in operation.

Expanding on this, the A107, can be used in as a nixie counter/Driver circuit. Here are schematics, for counting the full 0-9, and just 0-6:


The 0-9 counter is fairly simple, since the dekatron is made to divide-by-10. To divide-by-6, however, reset logic must be added, to force the count back to 0, just after it finishes with 5:



In this version of the circuit, the count transiently reaches 6 (Q7), which goes low, but not low enough to turn Q8 off, and therefore, leave only cathode “0” connected, and at the lowest potential of all cathodes. By adding two more transistors, Q7 will turn ON Q9, when it drops just below 20V. Q9 in turn, turns ON, Q10. Q10 is in the same phase as Q7, but it can fully saturate, and drop to less than 0.5V. This is more than enough to turn OFF, Q8.

Here is the video, of the Divide-by-10 version


Here is the video, of the Divide-by-6 version.

Analog Dekatron VU Meter

Instead of using a microcontroller, to convert an analog signal to a “bargraph” on a dekatron tube, this circuit uses only one “jelly bean” LM324 quad op-amp analog circuit to do this task. The microcontroller version is shown by my DoHickie Kit. This circuit on the otherhand, is purely an analog circuit. Below is the schematic:


Below are timing diagrams, showing its operation:


The diagram, above shows how the number of pulses, relative to the audio input level. Higher audio level, means more pulses. Next is how the pulses step the dekatron, with the glow RESET to K0, between samples:


After making the main circuit, an Idler circuit was added, to keep the glow moving when no audio is present, instead staying parked at K0. If the glow stays at any cathode for an extended period (hours to days, or more), the tube will suffer cathode poisoning, which presents itself on a dekatron as not stepping properly, or even completely stall.


Here are two video demonstrating this circuit:

Basic Operation.

With Idler Added.


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