On Thu, 2 Oct 2008 12:32:41 +0100, "N_Cook" wrote:

About 5 valves a year need replacing.

Very impressive. I thought it would be much worse.

IIRC about 1,000 of them are thyratrons, 2 are needed for each single bit of
memory storage. The mark 1 did not have them and required running 2 loops of
paper tape , the mark 2 required only 1 paper tape loop

That's cheating. Thyratrons are gas filled (usually hydrogen) low
pressure devices. They're also sometimes run with a relatively cold
cathode. The traditional failure mode is silicon and other impurities
in the filament slowly coating the cathode and ruining its ability to
emit electrons, is less of a problem with gas filled tubes such as
thyratrons. Thyratrons were probably chosen over the faster vacuum
tubes for that reason.

http://www.tnmoc.org/ColRbd.htm
"Mainly Mullard EF36 pentodes but also 6J5 triodes, 6V6
and 807 tetrodes and the GT1C thyratrons"

GT1C thyratron:
http://www.tubecollector.org/gt1c.htm
4V at 1.4A for the filament. So much for the cold cathode theory. I
guess that came later.


--
Jeff Liebermann
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