Soviet A-201 Polyatron Dekatron Tube  
Written by AnubisTTP on 2009-09-30  



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 encircling screen electrode provides an additional layer of protection against cathode poisoning, by collecting the majority of the sputter material from the cathode and preventing it from fouling the glass of the envelope. 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. Unlike most other Soviet glow transfer counters, which were manufactured at the Anod (Anode) factory, these A-201's were made by Plasma Labs, which is best known for it's lasers and high power transmitting tubes.


Soviet A-201 Polyatron Tube
Soviet A-201 polyatron counting tube.

Soviet A-201 Dekatron Tube
Though it resembles a dekatron, the A-201 has 30 anodes and a single cathode, operating inversely of a normal dekatron counting tube.

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