As far as heaters are concerned. I went to a lecture by Tony Sale of Colossus rebuild fame
How many valve failures a year, due to failed heaters in those 2,500, would you expect ? Please reply here
Answer tomorrow
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
In my field (audio amp repairs) actual valve heater failures are very rare - Occasionally you see a case where the contact between valve pin and internal riser is intermittent. I wouldnt like to guess at Colossus, maybe one or two, possibly none. Of course valves ain't what they use to be!
Ron
would
They are all old contemporary valves. I should have said how many failures for whatever reason in those 2,500 per year ? considering that they are powered up slowly from cold, to reduce that reason for failure .
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Get thee to a good reference library and examine issues of the Proceedings of the IRE from about 1945 through 1955 -- there will be a number of articles specifically addressing this issue, with solid numbers and derived mathematics, from research on test beds as well as data from Eniac and many other contemporaneous large digital machines.
Michael
About 100,000 hrs lifetime. No clue if that's mean, median, or average. Ignoring the bell curve and assuming burned-in tubes without infant mortality, that would be one failure every 40 hours for 2,500 tubes. With 8760 hrs/year, that's 219 failures per year.
However, that's not really true because the failures are not uniform. With new tubes, there's a peak for early failures (infant mortality), a long time with a very low failure rate, and then another big peak at end-o-life, where filament thinning turns them into fuses.
I recall stats from the original Eniac, that was initially experiencing a tube failure every 30 minutes of operation. Someone finally decided to reduce the filament voltage from 6.3VAC to about
5.9VAC(?), which extended the lifetime dramatically by reducing metal migration/thinning. Reduced filament voltage and temperature are not a great idea for power tubes, but are well tolerated by digital tube (flip-flop) circuits. I suspect Colossus uses a similar trick in addition to inrush current control.Predicted or actual tube life?
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
would
In the 40s Colossus was left on 24/7 on the recommendation of Tommy Flowers , Dollis Hill engineer, for maximum filament life.
Answer tomorrow will be what Tony Sale actually experiences in running the Bletchley colussus 7 days , only days , a week
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I seem to recall reading that during the service time of the original machine, not a single valve failed. Were they KT66s or 88s ...?
Arfa
Say, it runs 8 hours a day, every day... That is 2922 hours of operation a year. By rough estimate, every 5 years the complete valve supplement will be renewed. That is 500 valves a year. When it runs only 4 hours a day, it will be half this number, etc.
-- Met vriendelijke groet, Maarten Bakker.
I should have consulted both the life expectany figures of the tubes, and the rest of the thread before answering too late. Is 5 valves a year a long term average?
-- Met vriendelijke groet, Maarten Bakker.
Very impressive. I thought it would be much worse.
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.
"Mainly Mullard EF36 pentodes but also 6J5 triodes, 6V6 and 807 tetrodes and the GT1C thyratrons"
GT1C thyratron:
4V at 1.4A for the filament. So much for the cold cathode theory. I guess that came later.-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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