Mmmmmm LED operation is basically a bulk effect whereas the reliability of transistors depends more on surface effects.
In 1960 AT&T chose to go with Germanium, but the British Post Office chose the new silicon planar technology for future submerged cables. Previously Dr Gilbert Metson had written a landmark series of papers on valve (tube) cathodes. Extensive work was done at the Research Department at Dollis Hill in North London. The "good" tubes were found totally by accident in a batch of wartime manufacture (I believe they were an SP41 (I dont know the US equivalent) but its a 4v heater pentode.) As a result of this probably the first repeatered telephone cable was laid between UK and Norther Ireland in around 1944/45. The original repeaters had redundant sets of tubes, but it was found that this made the system LESS reliable, than just a single string of reliable tubes. I joined the PO sub cable transistor Group in 1961 and from scratch we laid the first oceanic cable in 1968 (I think) between Cornwall and Lisbon. The second was laid the following year between Canada and Bermuda. The last of the tubed cables was laid about the same time. The transistors were nothing special technically 400Mhz ft ( bit like the 2N916) but made with care and cleanliness and 75% of the build of each batch was destructively life-tested ( by my Group). By 1967 we knew we could meet the the tube system crtiteria of not more than one system failure due to a component failure in 20 years. In fact I think most of these system continued carrying traffic for near 30 years. I am not sure about LEDs, though some work was done in the 1970s on the efficiency degradation-rate in opto-couplers for the telecomms business..... that is a difficult one to accelerate easily....sting in the tail MTBFs are meaninless !! Slightly OT but "life" is measured as elasped time....so I claim immunity from flames!! Best Wishes Alan G3NYK ----- Original Message ----- From: "Poul-Henning Kamp" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Wednesday, April 30, 2008 6:12 PM Subject: Re: [time-nuts] LED reliability > In message <[EMAIL PROTECTED]>, Hal Murr > ay writes: > > >> LEDs been viable since at least the early 70's? Talk about planned > >> obsolescence... > > > >How reliable were the early LEDs? When did they start to get used in high > >reliability applications? > > Many of them are still happily emitting their faint red or green light. > > >The best reliability story I heard (many years ago) was about installing > >another trans-Atlantic telephone cable. They used tubes long after > >transistors were out. They knew how long the tubes would last. They didn't > >have much data on transistors yet. > > Actually, that's not entirely correct: They had reliability info > on transistors and they sucked. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > [EMAIL PROTECTED] | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
