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

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

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's ironic that some state that "rotating the tubes" is a waste of time, when Eimac stated (although they haven't made a 3-500Z in a very long time) that any tube older than one year is suspect -- thus implying you really need to use the tube within a year of its manufacture date.

    So, if someone bought a "spare tube" and let it just sit on the shelf unused, Eimac's policy was after a year the warranty would expire and if the tube doesn't work you're out of luck.:p

    Solution? Use the tube.

    When you have a spare, the only way to assure the spare works is to use it; and the only way to assure the "other" tube works is to use that one, also. In a single-tube amp you can't use them both at the same time, so cycling the tubes through the amp every year or so is the obvious solution.

    I agree some tubes seemingly last forever in storage or light use. But the 3-500Z is one commonly used tube for ham amplifiers that is of different design and construction than most of those "last forever" tubes. I've never had a shelf life issue with external anode ceramic tubes, and never had a shelf life issue with 4-400s, 4-1000s etc. either, but those are of very different design.
     
  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    I was quite pleased to find the tubes in my SB-220 to be just fine after that amplifier sat for god knows how long.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd be pleased, too.

    I think Eimac made some very good 3-500Zs (although I "heard" about a bad run somewhere along the line, not sure if that's even true) for many years, probably better than anything made today.

    But even they used to (dis)claim that after year, everything is suspect.:p

    Maybe marketing hype to sell more tubes. But there was probably an element of truth there.
     
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    All I know is it's easy to get a killowatt with 170ma grid current running the amp on 110V with 80W drive.
    The plate voltage is about 2900 no load and at a KW out the plate current is .67A.
    So they are good tubes.
    Oh and did I mention the amplifier has never oscillated during tune up on any band. :)
    So yes I am quite happy.
     
  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    To put it another way; the vacuum in a vacuum tube isn't perfect for a number of reasons.
    Glass and ceramics have a known leak rate, so do the seals.
    The materials used to make the elements off gas.
    Trace amounts of contaminants left over from when the tube was built are left behind.
    And finally;
    The vacuum system used to pump down the tube contaminates the tube by means of what is called "back flow.
    Vapors from mechanical pumps, diffusion pumps and cryo pumps leave trace contamination behind. The process is far from perfect. Most of these can be Gettered away into heavier compounds that have a lower vapor pressure.
    If you can turn the gas into a metal oxide it will stay that way until it gets hot enough again to separate out into it's components.

    While I haven't worked in a vacuum tube plant I have worked around high vacuum systems and I am well aware of the challenges involved in keeping the vacuum on the inside and the crud on the outside of a vacuum system, and that is all a vacuum tube is, a closed vacuum system of a sort.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Sounds like it's running well.

    I don't know how far you can push it with a 120V line (maybe not any more than you already have) but on 240V, you can run it up to 800mA Ip, and 250-300mA Ig wouldn't be excessive...I usually got 1200W output or a bit more with fresh tubes in an SB-220 on 240V.

    Just don't run it too long like that, the transformer is weaker than the tubes are.:p
     
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    The transformer is a concern, if its rated for 800VA continuous I would be surprised.
    240V isn't out of the question here I just have to get creative.
     
  8. KM1H

    KM1H Ham Member QRZ Page

    Dahl rated the original at 600va Sue and it is amazing how many hold up for years of contesting and DXing. Changing the filter resistors to 75-100K cuts down a little current and heat and a muffin fan on top in exhaust mode over the xfmr and caps extends life to some degree.

    Maybe Hammond will build a better one that fits the area.

    Carl
     
  9. KM1H

    KM1H Ham Member QRZ Page

    What unbelievable arrogance. One of the first rules of debate is that the participants show respect for each other and the only thing you respect is your reflection in a mirror. So dont expect any from others.

    No wonder so many challenge your knowledge which in some cases is totally wrong. Youre so self centered you dont even provide a name and must expect us to look it up.....sorry that doesnt work so your name will be Bozo for now.

    Also for your knowledge base, a tube does not age by excessive outgassing from the anode or seal leaks; that is called deterioation. And in a well built/designed/ tube that is run properly that will not happen until emission is down to the throw away point....that is called aging. My Eimac 3-500Z's are nearing 27 years and not a trace of gas because they are kept gettered in normal use and still run 1200W out.

    Anybody that has a gassy 3-500 of any make or an unknown that has been sitting for many years and does not want to chance using in his/her amp or regettering it please send it to me; I guarantee I will wind up with some good ones after processing. I'll also take the 211, 805, 810, 813, 814, 845, 861, 800, 8005, 4-1000, 250TH/TL, 304TH/TL, 450TH/TL, 750TH/TL, 6C21, and many other WW2 and later glass tubes which all have known gas issues. I'll even take 572B's.

    I will not accept any from Bozo; as far as Im concerned he is now a non person and should be treated that way by all until he grows up or until a moderator kicks him off.

    Carl
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    W0AIH used to use "Bozo" as his handle in Sprints where you exchange a name and signal report.

    I always thought that was cute. If nothing else, it's certainly memorable.
     
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