Interesting find on eBay - beam switching tubes (probably)

[Tomasz Kowalczyk]

During my routine search for interesting auctions I found this auction:

https://www.ebay.com/itm/Burroughs-6844A-Nixie-Tubes-on-PCB-Sockets-Leads-w-Counters-6703-5814a/192682396566?epid=1825418631&hash=item2cdcc40b96:g:Pf8AAOSw8U9burg8

The counter modules seemed suspiciously large, so I thought they might be non-semiconductor. And it seems it isn't a triode based digital system - in those large metal cylinders there are some unknown tubes. I think they might be beam switching tubes, as those required external magnet to work. 

The modules go by name CP-468/U, but I can't find any information about them.

This auction isn't mine and if I hadn't already spent lots of money on interesting and unnecessary stuff lately, I would probably buy it out of curiosity.
Also, the double triodes seen there (5814 tubes) might be worth a penny, as they seem to be a replacement for 12AU7/ECC82, popular tube in high-end amplifiers.

[David Forbes]

Those are definitely beam switching tubes. Tom Jennings has a similar version of one of those modules. This is a good price for a collector.

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[GastonP]

Actually, tubes used in binary counters have a problem known as "cathode poisoning" that is unrelated to the one of the nixie tubes. Apparently a resistive layer is formed on the cathode when the tube is kept long periods of time turned on but in "off" state, which renders the tubes useless for any kind of linear usage afterwards.

So the amount of money to be had from then is actually pennies :) . At least for the discerning buyers.

[Tomasz Kowalczyk]

In the last years of serious tube research and design there was a new type of cathode created, which was as efficient as previous types, but was immune to this effect. Most of tubes designed to be used in digital circuits were designed with long times with no anode current flowing.
We can't tell the switching tube type in this counter and tell whether it used the improved cathode or not, but 5814A datasheet from Tung-Sol clearly states that this tube "will tolerate long periods of operation under cut-off conditions". 

[John Rehwinkel]

In the last years of serious tube research and design there was a new type of cathode created, which was as efficient as previous types, but was immune to this effect. Most of tubes designed to be used in digital circuits were designed with long times with no anode current flowing.

There are a lot of myths about this, some disparaging metallurgy in the 1950s and 60s, referring to cathode impurities.  They are false.  The tube business, like any business, focussed on volume and cost cutting.  Early on, the tube manufacturers determined that adding a small amount of silicon to the (nickel) cathode sleeve accelerated the activation process, saving time and money.

Later, when computer applications came around, the "sleeping sickness" problem arose, where cathode interface would raise the cathode (and tube) impedance during long periods of cut-off operation.  A little research revealed that this was caused by the added silicon.

The tube manufacturers responded by offering "computer" tubes which were produced without the added silicon, and therefore required the longer (and more expensive) activation.  This worked fine.  To save money, the manufacturers would often use older tooling for the computer tubes, as linearity was not important.

Amusingly, a few modern audiophiles prefer the computer tubes, figuring they must be "better", but in some case, the computer rated tubes will be made with older tooling and have less linearity than the non-computer versions.

- John

[Tomasz Kowalczyk]

Thank you for correcting me and providing more information!