3-500 Taylor Graphite tube, need advise...

Discussion in 'Amateur Radio Amplifiers' started by KB4MNG, Mar 11, 2013.

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  1. KB5UBI

    KB5UBI Ham Member QRZ Page

    Use it or lose it. You're not going to hurt that 3-500 in and AL-80B and it should last years unless you baby it or don't turn on the AMP. Buy an extra in about 15 or 20 years from now.
     
  2. KM1H

    KM1H Ham Member QRZ Page

    It is obvious you know very little about gettering and the various types used and how they perform. Stop before you make an even bigger fool of yourself with all sorts of off the wall comments.

    Carl
     
  3. W1QJ

    W1QJ Ham Member QRZ Page

    A severly leaky tube that has lots of gas may never degas by activating the getter and running the tube with anode color. However a tube that may have a small amount of gas and does not show at 2KV but does at 3KV may very well be a candidate to have it's small amount of gas absorbed by the getter through a process whereby the tube getter is activated at low anode voltage and baising the tube to draw enough current to turn the anode red. After a given time the getter may absorb the gas. This has been proven by many. Carl has reported rejunvinating several 3-500z tubes with small amounts of gas. To me, that is proof enough that a tube can be degassed. it all makes sense. You seem to stand alone with your assumption that a tube can never be degassed. I disagee and so do others.
     
  4. W1QJ

    W1QJ Ham Member QRZ Page

    Will those who have successfully degassed a tube with the accepted method that prevails, please raise your hand. We know Carl has done it and W8JI claims he has too. I haven't so I can't say, but I am sure with hams being as cheap as we are somebody must have attempted bringing back a gassy tube. Anybody?
     
  5. W2VW

    W2VW Ham Member QRZ Page

    My experience also. With many tubes too. From here it looks like the 3-500Z gas story is a combination of bad quality control during late 80s, hams afraid of dissipating the tubes hard enough to getter and internet ham heroes who sit on websites exchanging stories.
     
  6. KD0CAC

    KD0CAC Ham Member QRZ Page

    I would have liked to think that documentation would have been shown by knowledgeable people before name calling :(
    Oh well this is where the internet seems to fail us .
    I have collected a bunch of 811's & 572's all used and " one of these days " :) wanted to billed a test-jig to apply the correct voltage & current to do some of my own testing ?
    The one of these days part is mostly gathering the parts & knowledge to build , I know that many would say just put in an amp and play , but my idea is to use the amp to do the testing while the jig is doing the process ?
    Finding ways to discredit old wives and piss off [ mad ] mothers :)
     
  7. WE6C

    WE6C Ham Member QRZ Page

    The main question should be, Can a bad tube damage a good amp? If not, doesn't hurt to try.
    anyone?
    Bob WE6C
     
  8. N2EY

    N2EY Premium Subscriber QRZ Page

    Depends on the amp and how the tube is bad.

    There are recommended mods for most amps that include "glitch resistors" and meter protection diodes. They are well worth doing. Here's why:

    Practically all modern amplifiers use silicon rectifiers and a capacitor filter in the HV power supply. The capacitor filter usually consists of a stack of high-value electrolytics in series, with equalizing/bleeder resistors. This sort of power supply has been common for more than 45 years, and has its good and bad points.

    In the case of bad-tube-in-a-good-amp, consider what can happen if there is a plate-to-grid arc inside a bad tube. If the capacitors are really good and fully charged, the peak current can be quite amazing. Or the overall plate current if a tube goes into thermal runaway. Such high currents can fry meters and possibly RF chokes and other components - and do it all before the primary breaker or fuse opens.

    73 de Jim, N2EY
     
  9. WE6C

    WE6C Ham Member QRZ Page

    Then I would say "it's not worth it" Old tubes should then be display models only.
     
  10. N2EY

    N2EY Premium Subscriber QRZ Page

    Not at all!

    Almost any modern amplifier can be modded with a few meter-protection diodes and a "glitch resistor" which will eliminate or at least minimize the possibility of damage should a tube arc or short.

    Just because a tube is old doesn't mean it's bad - it all depends on the particular bottle. I have seen used WW2 surplus power tubes deliver full power for years with no problems.

    And just because a tube is new doesn't mean it's good - it all depends on the particular bottle. Quality control of Chinese tubes is a roll of the dice - you may get a good one, or maybe not.

    73 de Jim, N2EY
     
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