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I was reading the story of Colossus, the first electronic computer which was used to decode Enigma, Tunny and Sturgeon codes during the second war. I came across a passage by Tommy Flowers the principal engineer in which he comments that "once we weeded out the odd misbehaving valve the machines ran without problems."
Heh, heh...Here's the good part...they were turned on in 1942 and turned off in 1944 and ran 24/7 for all that time at Bletchley Park. Goes to show I guess, that the "old valve" is pretty reliable. It's turning it on and off that creates thermal shock and therefore a few probs.
Regards,
Gary Jacobson
P.S. Colossus was in operation two year before ENIAC.
Follow Ups:
I remember reading history of the original US tube computers, where physicists would argue from the known tube lifetime that the statistical MTBF was too short to be useful.
The engineers responded by going to Sylvania to discuss tube lifetime issues. Sylvania improved the cathodes, resulting in the 7AK7 and other loktal tubes with improved lifetime.
vast arrays of 6SN7s, not sure if they were Sylvania or another brand. certainly the reliability of the tubes used was of critical importance in both machines
Steve
I sold a Fisher KX-200 that was restored to a good friend of mine several years back. It still using the same NOS Westinghouse tubes I got it with (which were used).
I've also got a pair of 1625 mono amps that sport a quad in each amp. I've had great results with this tube. I've got a large cache of these, all with dates codes from 1942 to 1944. So far, it is far and away my favorite power tube. Sounds incredible, with outstanding life like detail, great dynamic contrasts, low cost, and very long life. After all, the 1625 and 807 helped win the war. Much better than the current Russian/Chinese tubes (IMHO).
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
One of the bright moments for Polish mathematicians and cryptologist who broke the code in 1932 and re-constructed the Enigma machine.It was conveniently "forgotten" for 50 years or so along with Polish fighter Pilots who had a major impact on preventing German invasion of Great Britain and who in reward were denied participation in the great Victory Parade in London. Screw Britons and their politics...
Personally , after all these years I never had a tube product working without any issue (noise , popping sound , hum , tube failure etc etc) for more than 3 month straight including Audio Research gear which is built better than most.
Rgrds, W
Not only reconstructed the enigma, they also figured out at least 2 ways of breaking it, all by mathematical methods.
Regarding keeping tubeamps alive : good amps that does not run "on the limits" and good tubes ( well matched ) will happily run year after year.
I have a vta-70 at home with jj-6550 that i installed last spring, they still work fine.
You need to use good amps. Audio Research creates amps that have an appetite, and appetite for tubes. I rarely have a failure.
I have an ARC VT130SE that uses 8 6550s.
Previously it was on about 15-20 hours a week and I had to replace tubes (SED 6550s) about every 2 years (~1500 - 2000 hours).
I have now retired and listen about 30 hours a week, but with proportionately less switching on and off. This time my valves have lasted 3 years (~4500 hours) before one went - although the other 7 seem fine. The small tubes (Rocket logo 6h23n) have been fine for the whole of the last 5 years.
Conclusions? (1)This ARC amp is fine with these tubes; (2) switching on and off reduces life span; (3) or, I've just been lucky.
garf
I think that part of the issue with ARC is that they run tubes pretty hard and if people swap tubes without doing a good job setting the bias it can smoke them pretty rapidly. With many ARC amps, the bias is tricky to set.
The story of Colossus is a fascinating part of the book and British (BBC) TV series called "The Secret War". I know it's on You Tube if you want to see it - I have the book as well, I've read it at least 10 times.
Tubes/valves have two failure rate peaks - the first occurs in the time immediately following when they are put into service ("infant mortality") and the other at the end of their life of course. It's kind of like flying - the highest risk periods when flying are takeoff and landing. Tubes/valves have always suffered from infant mortality - even in Colossus, so don't be surprised when it still occurs today.
A year of continuous service is about 8800 hours, so with the first Colossus (there was more than one made) running just under two years from switch on to switch off it likely used the tubes for about 16000 hours. That is remarkable and is certainly in part due to the lack of turn on/turn off stress. And it operated without the stress of neurotic audio nuts like me obsessing about it and messing with it! :> )
Jim, good advise. Same is true with computer hard drives. I've kept my current computer on (24/7) since 2008. I just keep adding HD's, as needed. So far, so good.
All true, it is a fascinating story. I don't think I can afford the electricity bill for 24/7 power on though :)) I wonder if I can get a government agency to fund my audio habit?
I hear you. I don't have all my tube amps on 24/7. The AC bill would be exponentially outrageous. A nice slow-startup tube rectifier prolly helps dampen in-rush current flow to the other tubes. Like everyone else, I let the amp stabilize for a good 10-15 minutes before cranking it up. And keep the amp on, between sets or short breaks.
I like 6106 or 6087 rectifiers in my 5Y3GT powered amps, for their slow-startup and tough construction. I try to use NOS US made 5U4GB's in those amps that use this direct-heated rectifier.
The reason the Colossus machines were on 24/7 is because they were in use 24/7. Letting a tube home audio amp idle for such long periods of time is a waste of energy and tube (and other component) life.
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