3-500 Tube Life

Discussion in 'Amateur Radio Amplifiers' started by VK4TUX, Dec 2, 2011.

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  1. W8JI

    W8JI Ham Member QRZ Page

    This has gone past healthy education and now is just promoting some needless agenda.

    Eimac and others clearly give an acceptable filament operating range, it is right in the data sheets. Eimac clearly warns, if the voltage cannot be constantly regulated and monitored, to set voltage to stay INSIDE the nominal operating range.

    If AG6K and Adrian think Eimac is wrong, or want to rewrite what Eimac says, then do it for yourselves. But don't put other people's tubes or our bands at risk with splatter because you insist on using a method and voltages that no one else in the world says is proper.

    73 Tom
  2. N2EY

    N2EY XML Subscriber QRZ Page

    Yep. That's all there really is to it.

    73 de Jim, N2EY
  3. AG6K

    AG6K Guest

     Not quite Jim and Tom. The hazard of operating a Th-W filament at a potential More than 2% above the filament-V at the relative-P-out drop-off point is that the W2C (di-tungsten carbide) emissive layer will be evaporated faster than what's required to do the job, and will do so at an alarmingly exponential rate. So far there have been two references which indicate that a filament potential 3% higher than 2% more than the filament-V at the relative P-out-drop-off point reduces emissive life by 50%.
    On the other side of the coin, operating the filament at a potential Less than the +2% voltage does not cause un-reversible damage to the W2C layer.
    As I see it, Art Collins made the right call when he put a means of front-panel filament-V adjustment in Collins Radio amplifiers.
    • Rich, ag6k
    "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."
    — Mark Twain
  4. AG6K

    AG6K Guest

     Adrian and I think Eimac is right Tom. Eimac and the source Adrian quoted say that every 3% increase in filament-V above the recommended +2% set point reduces emissive life by 50%. My experiences and the experience of two Hams I know who do broadcast transmitter maintenance seem to confirm the advisability of following the +2% set-point procedure to get optimal tube life.
    As I said in "The Nearly Perfect Amplifier", adding a filament-V adjust pot would not add much cost, and it would result in a lot less W2C being needlessly lost.
    • Rich, ag6k.
  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    How many hours do you believe the average ham has his 3-500Z based amplifier on every year?

    And what is the published lifetime of for lack of any specs on the Chinese tubes...
    What is the expected life of an Eimac 3-500Z?
  6. AG6K

    AG6K Guest

     ... so Jim, if the pretend operator has already correctly set the tap for 3200vdc, then he/she subsequently measures 5.1V on the filament terminals on the 3-500Z socket, and moves the transformer tap up a notch to lower filament-V in order to increase emissive life,, doesn't the HV also decrease ?
    • Rich, ag6k
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    The pretend operator in question would follow the instructions in the manual and set the transformer taps to match her line voltage. She wouldn't set her transformer taps for 3200V on the plate voltage meter.
  8. AG6K

    AG6K Guest

     Since the filter caps total 3600 working volts, why is the limit 3200v Jim? - tnx
    • Rich, ag6k
  9. W1BR

    W1BR Premium Subscriber QRZ Page

    Because it gives some safety margin, perhaps???
  10. AG6K

    AG6K Guest

     a question that nobody could possibly know the answer to.

     There is no published lifetime. Emissive life of Th-W filament tubes depends on run-time and especially on operating potential. My 1967 3-400Z probably has quite a few operating hours on it since I used to be fairly active on the 40m Combat Zone before the Internet appeared. However, if the 3-400Z's fil-V had been 5.25 instead of 4.8, it would likely have run out of useful emission long ago since REL = (4.8v/5.25v)^23.4, or about 12% of what REL could have been at the lower-voltage.
    • Rich, ag6k
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