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Vacuum tube durability: Whose running the OLDEST tube ?

Discussion in 'Amateur Radio Amplifiers' started by WL7PM, Nov 24, 2021.

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  1. WL7PM

    WL7PM Ham Member QRZ Page

    ... There are a great many 572B, 3-500Z, 4CX1000a, and 8877 in daily, light duty amateur use.
    Some last for decades.
    Given careful usage, at rated power, " How long can a transmitting tube last ?"
    5000 hours ?
    20,000 hours ?
    More ?
    I have an Eimac 3-500 from 1994, still going strong.
    . Who's daily driving the OLDEST tubes here ?
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The Eimac 4-250 in my homebrew AM/CW rig I built in 1966 still works fine. I don't use it much today, but back then I used it every day. Probably has >>10,000 hours on it, not to mention just "age," since it's now 55 years old.

    The 811A RCA P-P modulators in that same transmitter are the same age, but they've been run at only 900V since day one, and I used CW a lot more than AM so they were mostly just burning heater power most of the time. But...they're still fine!
    MM0IMC and WL7PM like this.
  3. AF5XF

    AF5XF Ham Member QRZ Page

    I have some RCA 811s with 1959/1962 date codes.
    unknown hours when acquired.
    I made a 4 tube amp out of them.
    I used it hard on CW for several years.
    they are still going strong at approximately 500w output on 75m.
    MM0IMC likes this.
  4. K6CLS

    K6CLS Ham Member QRZ Page

    the Mackay console on the USS Red Oak Victory has several tubes with 1943 Navy dates. Everything works fine.
    WL7PM and WG8Z like this.
  5. WL7PM

    WL7PM Ham Member QRZ Page

    It appears that you have operational TUBES which predate the first known TRANSISTOR....
    Historical proof: "Tubes outlast transistors"....:)
    K6CLS likes this.
  6. G8FXC

    G8FXC XML Subscriber QRZ Page

    There are several failure modes for tubes. They contain a vacuum and have several ceramic to metal seals which will always be subject to some very small level of leakage - take a tube fresh off the production line, store it carefully and the chances are that in several thousand years it will no longer be a vacuum tube. It contains a heater - makes it effectively a light bulb and the filament will slowly degrade if powered up, even if the tube is idling. When the heater goes, it's junk even if the anode and cathode are in perfect condition. If you drive it hard, you'll heat up the anode - drive it hard enough and you will rapidly damage it, keep it within ratings and it will degrade slowly - becomes a question of what fails first? But you are quite right - a tube that was well manufactured in the first place and is subsequently used well within its ratings can outlast the early generations of solid state devices, at least...

    Martin (G8FXC)
    MM0IMC, WL7PM and AK5B like this.
  7. MM0IMC

    MM0IMC Ham Member QRZ Page

    I wonder what the longevity of NOS Soviet era valves (tubes) is like?
  8. W3SLK

    W3SLK Ham Member QRZ Page

    I got a pair of 805's in my AM modulator from 1939.
    AH7I likes this.
  9. K6CLS

    K6CLS Ham Member QRZ Page

    update: the oldest tube (1943) in the Mackay console is the 813! and we have spares of the same vintage.

    the 813s are just loafing along, though. rated for ~2500v on the anode, they get 1100v from the generator. but, the console runs the heaters biased by a few hundred volts (series, acts like a regulator), so voltage across the tube is 800 to 900, about 1/3 of its rating. so yeah, no wonder they last so long.

    word on the street is KPH has a PW15 from KFS, plate says Army Signal Core 1942. believed to be original parts. it is run at 5kW, so again just loafing along 8n retirement. we will do a closer check next time we can visit the site.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The >100 tubes in the original transatlantic communications (voice) cable which is almost as old as I am likely still work fine, although they decommissioned it to use fibre optic TA cables, so I guess we won't know.

    But they never failed and those repeater amplifiers in the original cable were placed every several km along its entire length from Canada to Ireland, so there's a lot of them. And although AT&T had just developed transistors, they didn't trust that new technology so they used tubes (probably smart, as the tubes operated at higher voltage and much lower current to accomplish the task, so the copper losses in the cable wouldn't be nearly as much).

    Assuming they're all still functional, they'd be about 66 years old now.

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