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3-500 Tube Life

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

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  1. AG6K

    AG6K Guest

     Possible but such caps are typically rated at 525V-surge / 450-Working-V. Maybe Tom R. knows the answer?
    • Rich, ag6k
  2. W1BR

    W1BR Premium Subscriber QRZ Page

    Surge voltage is not operating voltage. The surge voltage is usually specified in seconds.

    Here is the data sheet, again... for the 3-500Z:

    Recommended operating voltage is 5.00 volts, plus or minus 0.25 volts. Setting the voltage in a ham amp at the lowest
    voltage is foolish, since few hams have to means to accurately measure the tube performance as the tube ages, or to
    even measure the filament voltage--this has to be done at the tube filaments pins using a true RMS meter. Show us some
    graphs for a typical 3-500Z in ham service that shows filament voltages versus tube aging for IMD performance.

    I was a broadcast transmitter engineer for a few years back in the sixties (when TX engineers were licensed); and no one
    obsessed over the filament voltages for tubes in 4-400A power range. No one. The klystrons in our UHF transmitters, yes.

  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    So what you are saying is nobody really knows.
    If that's the case than without the physics to back it up Eimac and other tube manufacturers have no grounds to make such statements regarding filament / heater voltage VS tube life.

    You would think in the age of computer modeling this would be an easy question to answer.
    I'm not sure I accept your answer based on the level of understanding that exists regarding vacuum tube behavior.

    As an aside......
    My Ex and I use to listen to the goings-on in the forty meter and seventy meter combat zones.
    And no; my Ex didn't have a ham ticket he was a freebander.
  4. W1BR

    W1BR Premium Subscriber QRZ Page

    I should have also pointed out that the AM broadcast transmitters generally used high level plate modulation. They did not operate
    in Class B linear service. If the transmitter output was falling, their was engineer on duty was making hourly transmitter readings,
    and it would be noticed almost immediately. Modulation percentage was also monitored.

    In ham service the same tube would be producing IMD products across the band. Few hams are actively, or accurately able to,
    monitor power output or transmitter IMD performance.

    Suggesting that any 3-500Z amp will have extended tube life by lowering the filament voltage to 4.8 volts is foolish.

  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    I do want to make one comment regarding this discussion.

    First nobody is saying the you or statement regarding tube life is a lie.
    Nobody here is calling you a liar as you have said elsewhere Rich.
    What people are questioning is what is gained from going to all the trouble when tubes in amplifiers that are properly operated will last over fifteen years if the operator will simply take care in the setup and operation of the amplifier.

    Second; I was listening on the air this morning and heard what you said.
  6. N8YX

    N8YX Ham Member QRZ Page

    If it isn't the propagation gods frowning on me, it's the fact that I gotta go in to work early. I ALWAYS seem to miss the good stuff. :rolleyes:
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    Sometimes that's how it goes.
    We need to get a remote receiver for you to listen in on.
  8. AG6K

    AG6K Guest

     There is no need to monitor IMD or PEP, all one needs are:
    1. a means of adjusting filament-V.
    2. a relative RF-out indicator.
    3. a filament voltmeter of no special accuracy - or the ability to estimate c. 2% increase on the filament V adjust control.
    ---- The procedure: As you are reducing filament-V, when you see the RF indicator drop a skosh, stop, turn the filament-V adjust back up a bit and you're done.

     Correct Pete. If it's a factory-stock Henry 1KD-5 and the 3-500Z has 200 hours of run-time, nothing will ever make that 3-500 work fine. However, if the 1KD-5 is modified to reduce the filament-potential from 5.95v to 4.8v, the replacement tube should have >100 x more emissive life than the misfortunate original tube. [REL = (V2/V1)^23.4 = (5.95v/4.8v)^23.4 = 146.4]
    • Rich, ag6k
  9. AG6K

    AG6K Guest

     So my SB-220 foolishly runs the filaments at 4.8v? If it 's foolish why are my 1967 and 1981 vintage 3-400Zs still playing ok?

     a knowledgeable operator does not need to measure anything accurately to re-adjust filament-V optimally, all he/she has to do is to watch either an anode-I or a relative RF indicator and determine the point where the indication just begins to drop as fil-V drops - then stop, go the other direction a skosh or +2% on filament-V and he's/she's done for some time to come.

     hardly. When the filament-V is set according to the drop-point procedure, being able to accurately measure the actual V does not change the adjustment.
    • Rich, ag6k

  10. AG6K

    AG6K Guest

     Your question Susan: "How many hours do you believe the average ham has his 3-500Z based amplifier on every year?". Nobody could possibly know what Hams average because no such records are kept.

     Your question was about Ham behaviour, not vacuum tube.
    • Rich, ag6k

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