? About testing 572Bs , is this a viable method ?

Discussion in 'Amateur Radio Amplifiers' started by KD0CAC, Apr 30, 2012.

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  1. KD0CAC

    KD0CAC Ham Member QRZ Page

    I got some tubes that said to be tested , after receiving I tested with TV-7B/U .
    I do not have my list with me , but some were well below the min. some at min. & 1 above .
    tried all in equal pairs , and only the 1 above with another I had a reasonable output .
    So I emailed and asked what he did to test , and this was the response .

    quote -
    All tubes were tested while still on line.. Removed the HV from plate, Ohm meter is
    placed between the Cathode and the plate... A new tube will read between 2k -8k, anything
    above 50K has pretty much had it... these tubes read between 8k and 20K, 8K being the best and
    20K the worst. In this test, we were testing the actual conduction of the tube between the cathode (input) and the Anode(Plate output) the lower the resistance, the better the tube conducted.
    end quote

    To me that is just a short test , no output test ?
    John
     
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I don't even understand the test as described.
     
  3. KD0CAC

    KD0CAC Ham Member QRZ Page

    Thats why I posted his reply to how he tested , My tests with tube tester showed most tubes were below the min. in data book , then I tried all in amp in close to matched pairs , Yaesu FL-2100B that I got in unfinished repair condition .
    No output with tubes tested below min. 10-20 , low output with tubes near min. 36 , and near 500 watts SSB with tubes near 42 out of manual for TV-7U/B ,
    Using 811 test data chart , because no listing for the 572 ?
     
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Probably the best you can do. I don't see where an Ohmmeter can check anything except for shorts. Using a shorted tube can be very exciting.

    500W from the FL-2100B is about right (I've seen 650 out of them with new tubes, and that's about as far as it goes).
     
  5. KD0CAC

    KD0CAC Ham Member QRZ Page

    Steve ,
    I always do the shorts test with every tube , in tester before any other test .
    This guy is seller selling a lot on multiple sites including here , has a site for repairing amps etc. , I would expect more from him ?
    I am thinking about opening a dispute on PayPal , because it seems with all of the above , his claim of tested tubes an finding 1 out 5 being good ?
    And not knowing as much as I want to know , but trying / reading etc. , his test quote above just sounded like a shorts test to me .
    Thanks again John
     
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I wouldn't mess with used 572Bs unless they were free or very close to free.

    RF Parts has brand new ones with a very good warranty for $49.95/ea. They do test them, and they do honor the warranty.

    http://www.rfparts.com/572bprices.html#taylor

    For me, I'd rather have two new tubes than 20 used ones I have to sort through.:eek:
     
  7. KA9JLM

    KA9JLM Premium Subscriber QRZ Page

    Sounds like he is checking Mutual Conductance, same as a tube tester. But normally it is reading current and not resistance. Maybe a new trick for measuring.

    The gain of a 811 is not the same as a 572, As far as I remember.
    .
     
    Last edited: Apr 30, 2012
  8. KD0CAC

    KD0CAC Ham Member QRZ Page

    I do understand Mutual Conductance yet .
    But my guess , like I said earller , sure seems to me like a shorts test ?
    As far as comparing 811 & 572 , I'm not , the data for 572s is not in the book , if you have updated info on testing 572s in the TV-7B/U , I'm all ears ?
     
  9. KA9JLM

    KA9JLM Premium Subscriber QRZ Page

    OK.

    I thought you were using the 811 setting to test the 572. That would give you a lower reading.

    You could use a new 572 for good reference, but in circuit at the operating frequency is the best TRUE test.
     
  10. KD0CAC

    KD0CAC Ham Member QRZ Page

    I left out the - not - in my last statement , do not understand M.C. yet .
    With me leaving out important parts in a statement - " not " , the I also wander if we actually read before we reply , many times ?
    Face to face communication works much better for me , not having as much of a electronics background as would like to have had .
    If only I would have followed up , when I was handed a Heathkit catalog back in the early 60s :(
    Now the problem is , old farters , forgetting almost as fast as I'm learning , at this late date , doing catch-up .

    I was using the using the 811 setting !
    I did not get a new tube in any of these tubes I have .
    Still looking to see if there is a better listing for checking the 572s in my tube tester , since there is no listing in the manual for 572s ?
    73
     
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