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Glow Transfer Counting Tubes

For technical data, please refer to the Dekatrons of the World reference.

Glow transfer counting tubes, commonly known as dekatrons, are cold-cathode decimal counting devices. Dekatrons pass an ionization glow around a ring of cathodes by sending a single or offset double or triple pulse to intermediate guide electrodes, causing the glow to advance to the next cathode. Though a few dekatrons were manufactured with speeds as fast as 1 MHz, most were used for applications below 100 kHz. Dekatrons double as both counter and display; the count position is viewable through the top of the tube as a glowing dot. This combination of display and computation in a single component was not replicated in a solid state device until the introduction of LED smart displays in the 1970s.

Dekatrons come in three basic types: counters, computer counters and selectors. Counters have a single output cathode, which is pulsed once per full rotation. Computer counters have multiple output cathodes, usually four. Selectors have 10 output cathodes. Contrary to popular misconception, dekatrons were not widely implemented in computers. Only one computer is known to have made significant use of dekatrons, the AERE WITCH. Completed in 1950, the WITCH used large arrays of dekatrons for storage, and was a major consumer of Ericsson dekatrons until it was decommissioned in 1973.

The earliest and most common British and US dekatrons are 4 kHz neon-filled tubes. Faster dekatrons, in the 10-50 kHz range, are usually filled with argon or an argon-hydrogen mix, popular among hobbyists for the distinctive purple glow. Dekatrons rated at 100 kHz appear to be filled with some sort of Penning mixture which exhibits improved ionization characteristics, allowing for higher counting speeds. A small handful of dekatrons operate at 1 MHz; such tubes use hydrogen as the fill gas and typically have shaped cathodes and other internal complexities.

While most dekatrons are decimal counters, there are also a few base-12 counters, a handful of Soviet base-5 counters, and one binary counter, which operates like a flip-flop.

Mathetron

Invented in 1941 by Joseph Desch of NCR, the Mathetron was the world's first gas-filled ten-stage decade counting tube. More of a multistage thyratron than a glow transfer device, the Mathetron used a method of counting that could best be described as 'indirect glow transfer'. Each tube had a central cathode and 10 anodes, which were separated by a series of baffles. A transfer electrode was placed in the influence of each cathode and was paired with a gate electrode in the next counting stage by an external connection. In this manner, the charge from the active cathode would be transferred to the next, allowing the tube to preform a full base-10 counting operation. Encased in a large tubular envelope with over 30 external connections, mathetrons were extremely complex devices, and were used almost exclusively for the war effort. Desch counters were used in the Manhattan project, and Desch himself went on to head up NCR's Building 26, home of the top secret NCR project to decrypt Enigma-encrypted messages during World War II. The Mathetron was never made available for commercial use, and all known examples were destroyed after the war, along with the rest of NCR's cryptographic equipment.

Wales Counter

In 1947, inventor Nathaniel B. Wales designed and produced a new type of gas counter tube, which consisted of a series of three sheet metal anodes arranged in a vertical stack, each with 10 fingers. The top and bottom plates were bent in such a fashion as to align the tips of the fingers of each anode into a common plane. Two of the anodes acted as guides, and the bottom-most anode acted as the output ring. A ring cathode surrounded the anodes. Counting was performed by an offset double pulse directed into the guides, which would transfer the glow around the counting ring. A single output anode was isolated from the rest, providing a means to send a carry pulse to another tube. The Wales counter was a true top-view glow transfer counting device; all other glow transfer counters are direct descendants of its design. It appears that Wales was never able to obtain funding to mass-produce his tube, and no examples remain in existence. Had the Wales counter been commercially produced, it would have been a very low cost device to manufacture. The entire counting loop contained only five parts, most of which could be made from die-stamped sheet metal. In comparison, the typical Ericsson-style dekatron tube contains over 30 separate parts in its counting loop. Each cathode pin is a separate rod that must be welded or affixed to the support structure.

Dekatron

In 1949, Ericsson Telephone Limited sought to build a better counter. Given the trade name 'Dekatron', the Ericsson counter consisted of a counting loop of 30 cathodes spaced around a central anode. As with the Wales device, the glow was transferred around the counting ring by an offset double pulse that would transfer the glow sequentially from one cathode to another. The earliest Ericsson prototypes were not direct view, as the counting ring was covered by a mica support. However, by the time the tube went into production, this structure was dropped in favor of a direct-view configuration. Unlike previous developers, Ericsson put forth both the funding and research needed to make their glow transfer counting tube into a successful product. Within a matter of only a few years, Ericsson's Dekatron product line had ballooned into over 20 different distinct part numbers, and over a dozen companies jumped into the market with their own products.

Polyatron

The Ericsson-style dekatrons were, generally speaking, useful and workable solutions to the problem of high speed counting, as their widespread use would attest. However, traditional dekatrons have one significant flaw: if such a tube is left powered on with no input signal for an extended period of time, cathode poisoning from the active cathode will foul the adjacent cathodes, preventing the tube from counting properly. The proposed solution to this problem was the Polyatron, also known as an inverse dekatron. Counter to the dekatron's central anode and many cathodes, the Polyatron has a central cathode surrounded by 30 anodes. The motivation behind this alternate design is that by moving the glow discharge away from the counting ring, fouling of the electrodes could be prevented. Multiple Japanese and Soviet researchers simultaneously developed a Polyatron device in isolation, but the concurrent development of fast, stable transistor-based counters resulted in only one model of Polyatron ever being produced: the Soviet-made A-201. The A-201 has a ring cathode which is separated from its counting loop by a screen electrode, and can drive a Nixie display tube directly.

Elesta EZ10

If a dekatron and a pixie tube were fused together in some sort of horrible, The Fly-style matter transporter accident, a nomotron would probably be the result. Nomotrons function on the principles of glow transfer in the same manner as dekatron tubes do, but instead of relying on an external surround to indicate count position, a nomotron has a metal shield inside the tube which directly indicates count through punched or stamped numbers. However, even among the strange world of nomotrons, the EZ10 is unique. With its tiny miniature envelope and 50kHz counting speed, the EZ10 is the the smallest, fastest nomotron currently known. Like the more readily available EZ10A shown below, the EZ10 has 20 shaped cathodes, an argon fill gas, and a tiny 13 pin base. The pinouts of the EZ10 are somewhat different than the more readily available EZ10A, the guide cathodes are tied into even and odd groups instead of left and right groups, which prevents the tube from operating in a base-5 configuration. Unlike other nomotrons, the tiny mask plate at the top of the tube does not have any number markings. [View Detail]

Elesta EZ10A & EZ10B

Devices included in this entry: Elesta EZ-10A selector (13-pin miniature base; pictured in thumbnail) Elesta EZ-10B selector (13-pin miniature base) One of the most unusual counting tubes ever made, the EZ10A and EZ10B are unidirectional bent-cathode selectors in a miniature envelope. The EZ10A/B have a thirteen pin base, with three center pins surrounded by a ring of ten pins for each of the cathodes. The EZ10A appears to be an argon filled tube and has a rated counting speed of 300 kHz, while the EZ10B is filled with hydrogen, and is rated at 1 MHz. Both the EZ-10A and EZ-10B are single guide selectors with only 20 cathodes in their counting loops. The guide pins are split out and brought to two separate pins, with one pin for the guides on the left side of the tube and the other pin for those on the right. This makes it possible to use the EZ-10A and EZ-10B as both a base-5 and base-10 selector. It is of special note that the EZ-10B and ECT100 (pictured below) are the only two dekatrons confirmed to possess a full hydrogen fill, though some as-yet-unseen Soviet dekatrons are rated at 1 MHz, and are likely filled with hydrogen as well. [View Detail]

Elesta ECT100

The EZ10 may be strange, but the ECT100 is truly bizarre. The ECT100 is a 1 MHz bidirectional hydrogen-filled selector with only 20 cathode positions. This seemingly impossible feat is accomplished by a highly innovative internal design in which both guides and cathodes are driven with pulse waveforms. The tube has four distinct cathode structures, each of which is arranged as a ring of five spade-shaped posts connected to a central disk. Two of the cathode structures are designated as output cathodes, and the other two are designated as guide cathodes. In operation, the two output cathodes are driven with alternating waveforms and the two guide cathodes are driven with slightly delayed signals from the output cathodes. By reversing the connections between the output cathodes and the guide cathodes, the rotation direction can be reversed, allowing for a complete bidirectional base-ten count operation to be carried out in a tube that has only 20 cathode positions. With all of the ECT100's cathodes tied up as waveform inputs, a rather interesting method must be used to read the tube's state. Below each of the tube's output cathode spades is a forked sense anode, which projects upward around either side of the spade. When a given spade is ionized, the glow will exit from slits on either side of the spade, enveloping the sense anode. This causes a probe current to flow back through the anode, sensed on one of the ten output pins. The ECT100's combination of speed, function, and size make it, as far as we know, the most advanced dekatron ever made. Despite this, it was birthed into obsolescence, competing with the well-established beam switching tube and the introduction of small-scale integrated circuits. As a result, the ECT100 was narrowly implemented in its time, and is virtually nonexistant today. [View Detail]

ETL GC10B Series

Devices included in this entry: ETL / Baird Atomic GC10B counter (octal base; pictured in thumbnail) ETL GC10/4B computing counter (octal base) ETL CV1739 computing counter (octal base) This is one of the earliest models of dekatron, a 4 kHz neon-filled counter with 1 output cathode. Originally manufactured by Ericsson, the GC10B was heavily cloned by numerous European manufacturers and can be found in dozens of slightly different variants. The tube's distinctive tall narrow envelope and virtual immunity to outgassing make it a favorite among collectors. The GC10/4B is Ericsson's computing counter variant of the GC10B. The GC10/4B is identical to the GC10B in all important respects, with the exception of having four output cathodes available instead of the single output cathode of the GC10B. ETL GC10B, GC10B/S Datasheet (PDF) [View Detail]

ETL GC10D

The GC10D is a single pulse tube with three guides and forty cathode positions. The maximum counting speed is rated at 20kHz, but only when fed with a sine wave input pulse. When driven with a square wave, the maximum speed is only 10kHz. This is one of the most failure-prone dekatrons ever built; the tube's fill gas is over seventy percent helium, and is almost always absent by the time the tube falls into the hands of a collector. ETL GC10D Datasheet (PDF) [View Detail]

ETL GC10/4C

The GC10/4C neon-filled bidirectional counter is a later model British dekatron, no doubt intended to be a replacement for the GC10/4B. Though the GC10/4C is nearly identical to the GC10/4B from an electrical standpoint, it is quite different in construction. The tube abandons the long, phallic envelope common to previous Ericsson counters in favor of a short, compact envelope that is no longer than a standard octal tube. The 8 pin base is actually the same diameter as the tube envelope: the bottom of the glass envelope narrows to allow it to fit within the inside diameter of the base. The result is an aesthetically pleasing tube that will fit in any device designed for a standard-length octal tube, while still maintaining a distinctive shape. [View Detail]

Ericsson GC10/2P

Ericsson's sole entry into the miniature counting tube arena, the GC10/2P is a rather unusual device. This tube uses a unique construction style in which cathode and guide rings are constructed from single sheets of folded sheet metal, similar to the method employed by the 'Wales Counter' described above. The cathodes are held in a ceramic sandwich that confines the glow to the top portion of the tube, taken together the entire counting ring is much easier to manufacture than the complex arrays of welded cathode pins seen in many tubes. This tube is a bidirectional double pulse device, with a full 30 cathodes and a neon fill gas. The tube's 1khz counting speed puts it squarely at the bottom of the pack compared to other miniature counting tubes, though to be fair, many of those tubes are much less versatile unidirectional devices. The GC10/2P was a rather short-lived tube, and it is fairly rare as a result. ETL GC10/2P Datasheet (PDF) [View Detail]

ETL GS10C Series

Devices included in this entry: Baird Atomic GS10C selector (duodecal base; pictured in thumbnail) Amperex Z502S selector (duodecal base) ETL / Baird Atomic dual logo GS10C/S selector (duodecal base) The GS10C is the counterpart to the GC10B, a basic 4 kHz selector with a neon fill gas. Though originally made by Ericsson, the GS10C was manufactured by innumerable companies under different part numbers. The GS10C/S is identical to the GS10C in every observable characteristic, but is 'designated for military use'; Ericsson-ese for 'more holy water'. ETL GS10C/S Datasheet (PDF) [View Detail]

ETL GS10E

The GS10E, despite its pedestrian appearance, is a quite rare tube; as it appears to be the last model of dekatron ETL manufactured before switching over to compact envelope counting tubes. In outward appearance this tube looks like a standard ETL bidirectional selector with no shade ring, there is no obvious enhancement to explain the existence of this part within ETL's vast array of dekatron products. This tube appears to use some sort of Penning mixture, the exact gas mix is unknown, but the tube illuminates with a pale orange hue that is noticeably different from the earlier neon filled ETL tubes like the GC10B. The tube's 10Khz counting speed is slower than the hydrogen-rich ETL high speed tubes, but faster than neon filled tubes like the GS10C. The near total lack of GS10E's in the tube collector marketplace suggests that very few units were actually manufactured. [View Detail]

ETL GC12/4B

The GC12/4B is a counting tube oddity: a 'dekatron' that is designed to count in base-12 instead of base-10. Base-12 tubes served an important niche function, since the hour of the day is typically measured in 12 or 24 positions, they allowed designers to save an entire tube in any device that measured the time of day. The GC12/4B is a 4kHz bidirectional counter with a neon fill gas, and is in every way identical to a GC10/4B with the exception of six extra cathodes in the counting loop, to allow for a divide-by-12 function to be carried out in a single tube. The explosion in popularity of nixie clocks and similar devices has made these tubes rather hard to get, as they are hotly contested in the open market by hobbyists for use as hours indicators in dekatron-based clocks. ETL GC12/4B Datasheet (PDF) [View Detail]

ETL GS12C
	The GS12C is the near ultimate evolution of ETL's original dekatron formula: a base-12 selector with a maintenance base. This unusual base allows for connection of wire leads directly to the base of the tube, without any need for a socket. [View Detail]

ETL GS12D

Devices included in this entry: Baird Atomic GS12D selector (modified duodecal base; pictured in thumbnail) ETL GS12D selector (modified duodecal base) The GS12D is a base-12 selector in a standard Ericsson selector envelope... with a twist. It is impossible to fit all the pins necessary to preform a full base-12 selection function onto a duodecal base; the GS12C shown above solves this with the use of a 'mainteinence' style base, but glow transfer tubes do fail after a while, and the direct solder connections of the GS12C make replacement a chore. The GS12D abandons the maintenance style base in favor of a duodecal base with two extra flying leads that exit from either side of the base. The flying leads control the tube's guides; all of the other pins on the base being consumed by output cathodes and the tube's anode. The GS12D is a neon filled tube, and it's maximium counting speed is the 4kHz that one would expect from a neon filled dekatron. Base-12 tubes are heavily sought by nixie clock hobbyists for use as hours indicators in various clock projects. The GS12D will serve for this function, but the combination of the need to solder directly to the tube's flying leads and the rarity of duodecal sockets make the tube less than ideal for this purpose. ETL GS12D Datasheet (PDF) [View Detail]

ETL GCA10G & GSA10G

Devices included in this entry: ETL GCA10G direct-drive counter (modified 17 pin base) ETL GSA10G direct-drive selector (modified 27 pin base; pictured in thumbnail) These strange devices are known as 'direct drive' glow transfer counting tubes: dekatrons specially designed to be coupled to a Nixie display tube without any intermediate hardware. The GSA10G has a series of ten supplemental anodes arranged equidistantly around the inside of the tube, one for each output cathode. Nixie tube cathodes are connected to these anodes, as the glow transfer passes by a supplemental anode the flow of current will jump between it and the primary anode, causing the appropriate character in the Nixie tube to illuminate. The primary anode has a series of fins around it's perimeter, which isolate the glow transfer to specific supplemental anodes during operation. The GCA10G is an earlier counting-only variant of Ericcson direct drive technology, and lacks many refinements, such as the finned primary anode and curved secondary anodes. (GCA10G's with late date codes seem to adopt these features.) The GCA10G's lack of selector output cuts the pins on the base down to 18, compare this to the GSA10G, which has a monstrous modified 27 pin base with an extra pin in the center of the socket. Unfortunately the GSA10G and GCA10G were a technology that few actually felt was necessary. Dekatrons already directly indicate their count position, and few felt the substantial additional cost of a Nixie tube was worth it just to give counter operators an Arabic character to stare at. Very few direct drive dekatron part numbers were made and fewer still were used in products. The GSA10G example shown here is actually an Ericsson development sample; the label includes terse warnings about the lack of future supply. ETL GSA10G Datasheet (PDF) [View Detail]

Mullard Z302C

The Z302C is one of the only dekatron tubes manufactured by Mullard that was not merely a clone of a more popular Ericsson part number. It's internal construction is somewhat unusual, as Z302C tubes are designed to be directly coupled into multi-stage counters with no intermediate active components. Though the tube has 30 cathodes it is not intended to be driven in a 2-guide fashion, as the tube only has one set of guides, located in the first position after each main cathode. The second electrode positions are designated as 'extinguishing electrodes' and are wired in two groups, based on whether the given extinguishing electrode precedes an even numbered cathode position or an odd numbered position. In normal operation the extinguishing electrodes are not tied to a phase shifted version of the input pulse signal, they are driven by the successive charge and discharge of an external capacitor network. The zero position extinguishing electrode , shown in the inset photo to the left, sits outside the count loop and is tied to a -300 volt supply. When the glow transfer reaches the zero position electrode, the sudden increase in current draw produces a pulse at the anode of the tube, which can be directly propagated into the guide of an adjacent counter. Overall, this system of counting is rather clumsy, requires a separate -300 volt supply, and limits the tube's count speed to a mere 1kHz. The tube can be driven in a normal two-guide fashion by tying all the extinguishing electrodes together, but it should be noted that all commonly available dekatron drive circuits can only drive this tube in a counterclockwise direction. Clockwise counting is impossible because the gap in the counting loop at the zero cathode position prevents the glow from transferring properly. [View Detail]

Mullard Z504S Series

Devices included in this entry: Mullard Z504S selector (13-pin compact base; pictured in thumbnail) Mullard Z505S selector (13-pin compact base) The Z504S and Z505S are European 13 pin double pulse selectors in stubby compactron style envelopes. The Z505S is significantly smaller in dimensions than its American made counterparts like the 8035, but can only count at 50kHz compared to the 100kHz counting speed of the 8035. The example we have has unfortunately lost its fill gas, but in operation the tube would have glowed orange, suggesting some sort of mixed gas Penning mixture. The Z504S is the standard 4kHz counterpart to the Z505S and is identical in envelope and internal construction other than its more stable neon fill gas [View Detail]

Raytheon 7978 & 8262

Devices included in this entry: Raytheon 7978 selector (13-pin compact base) Raytheon CK8262 selector (engineering sample,13-pin compact base; pictured in thumbnail) Though Raytheon manufactured many second source variants of Sylvania dekatrons like the 6802 and 6910, Raytheon developed few new dekatron part numbers themselves. The hard to find 7978 and nearly unobtainable 8262 are the only two dekatrons existent that were manufactured exclusively by Raytheon. With the exception of its pedigree the 7978 is otherwise a fairly standard neon filled compact dekatron, it operates in a conventional double pulse fashion and counts at 5kHz. The tube's electrical characteristics are very similar to a Sylvania 8353, though its envelope and pinouts are different. The 7978 tube is substantially rarer than an 8353 however, and heavily sought by collectors seeking a example of a Raytheon-manufactured tube. The 8262 is Raytheon's high-speed counterpart to the 7978, it's strangly colored mixed-gas fill is responsible for the tube's brisk 100kHz counting speed. The 8262 is so rare as to practically only exist in the annals of tube lore, but as a counting device it is probably best left to the crushed velvet shelves of tube collectors. Raytheon's high speed decade counter gas has a notorious habit of vacating a tube's envelope long before the tube falls in the hands of a modern hobbyist, which makes the 8262 an extremely poor choice for a dekatron-themed project. Raytheon 7978 Datasheet (PDF) [View Detail]

RFT Z562
	A German made compact envelope dekatron selector. The Z562 is a neon filled tube very similar to the Sylvania 8353, but has a faster maximiun counting speed of 5kHz. The taller than average envelope of the Z562 has a high domed top and heavy shade ring, this tube is a rare but visually appealing choice for use in a project. [View Detail]

Rodan DK23

Even the Japanese joined the dekatron market with tubes like the DK23, a single-pulse counter with three guides and forty cathode positions. Counting speed is rated at a capable 20 kHz and the fill gas is unknown, but appears to be some sort of Penning mixture consisting of a melange of hydrogen, neon, and other trace gases. Though difficult to find, these tubes are much more robust than ETL's single-pulse GC10D, and rarely fail from outgassing. Rodan DK23 Datasheet (PDF) [View Detail]

Rodan DK24

Another uncommon Japanese counting tube, the DK24 is Rodan's selector counterpart to the single-output DK23. The most striking feature of the DK24 is its unusual base, a 14 pin loctal style with a metal keying post and ring epoxied to the bottom of the tube. The DK24 has similar specs to the DK23; single pulse configuration with forty cathodes, a 20kHz counting speed, and a Penning style fill. [View Detail]

STC G10/241E

The G10/241E, made by STC, is a fairly standard representative of the nomotron form factor. The G10/241E is a unidirectional tube, with angled sheet metal cathodes hidden under its metal shroud. Unlike many other unidirectional tubes, the direction of the glow transfer is not controlled by the slant of the cathodes. Instead, each guide cathode has extremities constructed of different alloys with different maintaining voltages. These multi-alloy cathodes are reported to substantially increase the count accuracy of the tube, but require numerous additional external components in the form of resistor-capacitor networks attached to the guide cathodes. The count position indicators on this tube are not stamped on the metal, but rather printed on a mica disc mounted above the shroud. The tube has a stubby wide envelope and an attractive metal duodecal base. It should be noted that the metal shield of this tube almost completely blocks view of the glow discharge, rendering it nearly useless as a display device. STC G10/241E Datasheet (PDF) [View Detail]

Sovtek OG-3
	The OG-3 is a single-pulse dekatron with 40 cathodes and an unusual extra output cathode. 20 kHz counting speed, argon fill, octal base. The OG-3 is currently the most common dekatron in the world, as Soviet surplus floods the international market. This example is a somewhat rarer metal base variant. Soviet Dekatron Datasheet (PDF) [View Detail]

Sovtek OG-4 Series

Devices included in this entry: Sovtek OG-4 counter (octal base; pictured in thumbnail) Sovtek OG-7 counter (octal base) Sovtek OG-9 counter (octal base) The OG-4 is a double-pulse, bidirectional counting tube with a neon fill gas. The OG-4 is a very slow dekatron: it has a rated counting speed of only 2 kHz. The OG-7 is identical to the OG-4, but with an argon fill gas. The OG-7 also has identical pinouts and internal construction as the OG-4, but its counting speed is rated at a brisk 50 kHz. The OG-9 is similar to the OG-4 in appearance, but is a 'computing' tube with multiple output cathodes. All of these tubes were manufactured in both bakelite and metal base variants. Sovtek OG-4 Datasheet [View Detail]

Sovtek OG-8

The OG-8 is a very unusual high speed counting tube. The tube is a single guide, unidirectional design with a metal octal base. The tube has 20 bent cathodes under a heavy shade ring, five of which are brought out to individual pins on the base. The tube's rated counting speed is 100Khz and the fill gas in unknown, though it appears to contain a mix of argon and other gases. OG-8 Datasheet (PDF) [View Detail]

Sovtek A-101 Series

Devices included in this entry: Sovtek A-101 selector (13-pin base, pictured in thumbnail) Sovtek A-102 selector (13-pin base) Sovtek A-103 selector (13-pin base) The A-101 is Sovtek's basic neon filled selector dekatron, a double pulse selector with an unusual 13-pin base. Rated at a mere 1kHz, the A-101 is one of the slowest dekatrons ever made. The A-101 design saw improvements in the A-102, which introduced an argon fill, and the A-103, which incorporates some minor internal changes. Soviet Dekatron Datasheet (PDF) [View Detail]

Sovtek A-108 Series

Devices included in this entry: Sovtek A-107 selector (12-pin miniature base) Sovtek A-108 selector (12-pin miniature base) Sovtek A-109 selector (12-pin miniature base; pictured in thumbnail) The Sovtek A-107, A-108 and A-109 share a highly important pedigree, they are the smallest dekatron part numbers in the world. Packaged in the same envelope as an IN-2 nixie tube, each is tinier than even Elesta's minuscule ECT-100 selector. The unusual qualities of the A-107, A-108 and A-109 do not end with size however. Unlike most dekatrons which count in base-10 increments, these units are base-5 counting tubes. The structure comprises ten shaped cathodes that can either act as output cathodes or guides, these units are unique among the world of dekatrons in that every cathode is brought out to a separate pin, half of the cathodes must be tied together to form a guide for counting operation. The shaped cathodes limit the tube to unidirectional counting, but maximum counting speeds are quite respectable; the neon filled A-108 and argon filled A-107 can both count at up to 10kHz and the mixed gas A-109 will count at up to 100kHz. The A-107 has an additional oddity, it is not a direct view device. The A-107's counting loop is completely covered with opaque silvering and the glow transfer can not be seen under normal light levels. The Soviets did have a scheme to use this tube as a base-10 counter, in which no cathodes were designated as outputs. To pull it off, even and odd number cathodes were each fed half of an out-of-phase signal from a flip-flop circuit. Standard dekatron offset guide pulses will not work for this, the signals on the even and odd numbered cathodes must be exactly 180 degrees out of phase for the tube to count correctly. Such a system was highly impractical, as it required a transistor across every cathode that needed to double as an output as well as the active components necessary to generate the flip-flop signal. Soviet Dekatron Datasheet (PDF) [View Detail]

Sovtek A-201 'Polyatron'

Though the A-201 looks similar to a dekatron, this strange device is actually a polyatron tube, also known as an inverse dekatron. The A-201 operates in reverse of a normal dekatron; the tube has a ring of ten anodes surrounding a central cathode and an encircling screen electrode. The polarity of all supply voltages and incoming pulses are reversed, and removal of the tube's cathode from active participation in the counting process prevents the cathode poisoning that can foul normal dekatrons. The A-201 is not designed for direct view of count position, as the glow transfer occurs in a slot approximately halfway down the length of the tube. Much like a magnetic beam switching tube, the A-201 can be directly coupled to a Nixie display for indication of count position. However, the A-201 is slow compared to its dekatron contemporaries: the tube's maximum counting speed is only 10kHz. [View Detail]

Sylvania 6476A
	Early USA-made neon filled selector. This tube is double guide, with a 4kHz counting speed and a B12E (duodecal) base. Sylvania Decade Counter Tubes (PDF) [View Detail]

Sylvania 6802 Series

Devices included in this entry: Sylvania 6802 counter (octal base) Raytheon CK6802 counter (octal base) Sylvania 6909 counter (octal base; pictured in thumbnail) The 6802 is Sylvania's original octal-base counter, designed to compete with ETL's GC10B. Sylvania later upgraded the 6802 design to the 6909, which replaces the neon with a Penning mixture and is capable of impressive 100MHz operation. Unfortunately, the 6909 is extremely prone to outgassing, making the 6802 ultimately a much more practical and long-lived device. Raytheon made second-source versions of these tubes, prefixed by a CK identifier in the part number. The CK variants of these tubes are electrically identical, despite their vastly different internal construction. Sylvania Decade Counter Tubes (PDF) [View Detail]

Sylvania 6910

Devices included in this entry: Sylvania 6910 selector (duodecal base; pictured in thumbnail) Raytheon CK6910 selector (duodecal base) The 6910 is an ultra high speed selector with a Penning fill and a 'duodecal' B12E base. The 6910 is one of the few 100 kHz bidirectional selectors known to exist. Unfortunately, all of Sylvania's 100kHz dekatron types are extremely prone to outgassing. As with the 6802 and 6909, Raytheon made a second-source version of this tube that was prefixed by a CK identifier in its part number. Sylvania Decade Counter Tubes (PDF) [View Detail]

Sylvania 8035 / CT-4251 Series

Devices included in this entry: Sylvania 8035 / CT4251 selector (13-pin compact base; pictured in thumbnail) Sylvania CT-4251 selector (13-pin compact base) Sylvania 8353 selector (13-pin compact base) The 8035 is a high speed selector tube in a small compactron-style envelope. The 8035 has a Penning fill gas and a maximum counting speed of 100 kHz. The tube has a standard 13 pin base, and will fit in both 13 pin Nixie tube sockets, and 20 pin sockets like those used for the 6167 and MO-10R counting tubes. Early internal versions of this tube are only marked with the CT-4251 Sylvania internal part number, and lack the 8035 designation. Sylvania also released the 8353, internally identical to a 8035 but with a neon fill. [View Detail]

Sylvania 7155 Series

Devices included in this entry: Sylvania 7155 computing counter (7 pin base; pictured in thumbnail) Westinghouse 6879 computing counter (7 pin base) The Sylvania 7155 is an unusual tube: a 100kHz double pulse bidirectional counter in a miniature envelope. The 7155 is one of the smallest, fastest dekatrons ever made, surpassed only by the most advanced Elesta and Sovtek dekatrons. The 7155 is filled with a Penning mixture; Sylvania also manufactured a neon filled version of this tube, the 6879. The example included here is a Westinghouse manufactured second source variant of the 6879. Sylvania Decade Counter Tubes (PDF) [View Detail]

Western Electric 6167

The 6167 is another very unusual counting tube. Instead of having pins or bent cathodes like most other dekatrons, the 6167 uses tiny springs for its cathodes. Each spring has a small finger, which exits the top of the spring and hangs over the center of the adjacent cathode. It requires less maintaining voltage to hold a glow discharge within a tube-shaped cathode than upon the surface of rod-shaped cathode, and the 6167 is designed to take full advantage of this phenomenon. During operation the glow will rest in the center of each spring, jumping to the finger only during glow transfer. The 6167's unusual cathode construction makes it a unidirectional tube, with ten output cathodes and ten guide cathodes. The guide cathodes are spit into two groups of five, to allow for base five or base ten counting. The tube actually has 21 cathodes: a single "zeroing" cathode sits outside the counting ring and feeds into the first count position at an angle. The tube can be reset to the zero position by pulling the zeroing cathode to ground without interrupting the counting loop. The tube also has a supplemental anode, which sits between the normal anode and the final output cathode in the counting loop. This anode is used to provide a carry without interrupting the counting loop - the supplemental anode is pulled low as the glow transfer passes by it. It should be noted that even though this tube uses an unusual 16-pin base, it can be used with normal Cinch 13-pin nixie tube sockets due to the cylindrical void located in their center. The 6167 will also fit 20-pin sockets like those used for the MO-10R beam switching tube. Western Electric 6167 Datasheet (PDF) [View Detail]

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