| Glow Transfer Counting Tubes |
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 1MHz, most were used for applications below 100kHz. 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 would not be replicated in a solid state device until the introduction of intelligent LED 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, each of the WITCH's memory stores contained 90 GC10A dekatron tubes; the WITCH was a major consumer of Ericsson dekatrons until it was decommissioned in 1973.
The world's first production glow transfer counting tube, the short-lived GC10A, was filled with helium, but all other early and common British and US dekatrons are 4kHz neon-filled devices. Faster dekatrons, in the 10-50 kHz range, are usually filled with argon or a helium-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 1MHz; 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 unusually constructed Soviet base-10 dekatrons which can also function as base-5 counters, and one binary counter, which operates like a flip-flop. |
| Elesta ECT100 |
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The ECT100 is a 1MHz 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 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] |
