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? 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 ?
  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.

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

    KA9JLM Platinum Subscriber Platinum 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 Platinum Subscriber Platinum Subscriber QRZ Page


    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 ?
  11. KA9JLM

    KA9JLM Platinum Subscriber Platinum Subscriber QRZ Page

    It is a bummer that you got sent some bad tubes.

    Can you share who you bought them from so we can steer clear ?

    Your tester seems close if you are getting a reading of 42, on the 811 settings. A good 572 may read a little less and be considered good. 36 is good for the 811. The only difference in the 572 and the 811 for that tester will be the reading that you get. Everything else will be the same setting.

    You may want to let the seller know, and get some new ones, without getting paypal involved. I would try that first.

    Good Luck.

    Last edited: Apr 30, 2012
  12. KD0CAC

    KD0CAC Ham Member QRZ Page

    Well I may post his info , but several issues 1st , not knowing enough to be sure of all the facts , thats why the thread .
    Then after gather more info , the thread .
    Then getting back to him with what I think I learned and try to settle any issues with the deal .
    Then lastly involving PayPal .
    But with him having a lot of sales , and repair site in the net , I would hope he would have better info than me ?
    The last thing I would want to do , is make accusations with my ignorance of the subject .
    Thanks again
  13. KA9JLM

    KA9JLM Platinum Subscriber Platinum Subscriber QRZ Page

    It does seem that the seller needs a better way of checking tubes.

    Normally a tube tester will tell you if a tube is bad, But may not tell you for sure if it is good.

    When a tube is in the operating circuit it may operate different than in a tester.

    All the tubes should check about the same in your tester, if they are close to good.
    Sounds like you did get some duds. That is a chance you take when you buy used parts.

  14. KD0CAC

    KD0CAC Ham Member QRZ Page

    Without reading what I have posted , I take a chance and restate .
    I got 5 tubes from the one guy , and 2 tubes with no claims from the other guy I traded the amp for .
    The 2 that came with the amp , 1 was a chineez that tested at 19 , the other a Centron that tested at 42 .
    Then the set of 5 were Penta -10 , Ratheon -32 , Centron red label -32 , Centron red label -36 and Centron blue label 46 .
    These were using the data book for 811s on the TV-7 .
    Then since this was an unknown amp , repairs not finished by the last guy , and never worked since he got it , I used the lowest rated tubes , in match pairs just incase , to not damage good tubes and got response from amp , but no output - did not expect any .
    Then tried middle rated , 32s very little output , good sign the amp is OK now .
    So used the best tubes - 42 & 46 and got output of about 450 watts SSB , so now the amp seems good , but I am going to check the tuning coils , and have a couple tubes .
  15. KD0CAC

    KD0CAC Ham Member QRZ Page

    Well except for my results of no output for the tubes in question , now I am not sure again .
    The latest explanation of his testing sounds good to me ?

    quote - " Not testing for shorts. A tube is just like a transistor, only its high impedance instead of low.
    When the filament heats the cathode, electrons will flow to the anode (Plate). As the signal increases on the cathode, it is amplified by varying the plate. The test I did showed how much the tube would conduct. As the resistance went lower, the tube was conducting harder. (sign of a working tube.) Again, each tube was tested in circuit this way. A transistor works the same way, only no filament... signal is applied on the base. a bias voltage is applied to the emitter, bias's the the transistor on and the collector amplifies the signal. This is the simple definitional, but describes the basic operation. Have been involved in electronics for almost 50 years now, and all circuits work pretty much the same way. "
  16. WA7KKP

    WA7KKP Ham Member QRZ Page

    I think you're simply measuring the conductance of the tube while driven with a signal . . . the poorer the emission, the higher the resistance.

    The best way to check any power handling tube is to sub it into a working amplifier circuit, and note grid drive and plate current, and measure RF output with a good calibrated wattmeter (IMHO that translates into a Bird 43). Generally, as these tubes age, the emission drops and the output goes with it.

    Since most of these tubes are capable of more than 50-100 ma plate current, the average tube tester doesn't test with this high of current. Only the amplifier (circuit) does . . . .

    That what we do in broadcasting -- check 'pulls' against a new tube, and keep the ones that work, albeit at the lower end of their useful life.

    Gary WA7KKP
  17. VK6ZGO

    VK6ZGO Ham Member QRZ Page

    It sort of makes sense,in that,all an Ohmmeter really consists of,is a voltage source with an ammeter in series,calibrated in resistance,instead of amps,or milliamps.
    If you ran the filaments & connected the Ohmmeter with the lead producing a +ve voltage on the anode,& the other lead on the cathode with no bias on the grid,the thing should give a reading of some kind.
    A DMM probably wouldn't work,but an old analog one would probably do so,as the test voltage is higher.
    You could then measure a good tube,& compare the bad ones,but the whole idea freaks me out.It seems very much reliant on guesswork!

    WA7KKP's method is a good one,& is indeed what is used in Broadcasting.
    In all my years in that field,I have never seen a gadget for testing transmitting tubes,(apart from little ones,like 6146s,which can be tested on normal tube testers).
    We always tested them in the Transmitter.

  18. K5DUT

    K5DUT Ham Member QRZ Page

    95% of tube testers cannot properly test power transmitting tubes such as 572's 811's etc. They are not capable of loading the tube under test heavy enough to test its power output and gain. I see lots of claims of tubes tested with ohm meters etc.... worthless test! Buyer beware.

  19. K5DUT

    K5DUT Ham Member QRZ Page


    with the prices of some ham fest special transmitting tubes reaching over a kilobuck, a means of testing them on site it handy.
    I have a homebrew portable transmitting tube tester that consist of a small 40 meter transmitter and multi socketed amplifier to plug in most popular transmitting tubes and test them on site. you must have 110 ac available, which most hamfest do.

    It loads and test tubes to the 5 to 600 watt level which is a reliable test. One guy came up at a hamfest with a big ceramic tetrode with handles on it and ask me to test it. I grinned and pointed down the street to the local broadcast station and said "try them".

    73, Don.
  20. KE3WD

    KE3WD Ham Member QRZ Page

    The common "tube tester" - whether it incorporates the mutual conductance method or not - simply does not have what it takes to truly test a transmitting tube.

    The tube tester, can, however, serve as a good Go-NoGo screen before inserting tubes into a real transmitter into dummy load to check output and its a good idea to perform such tube check first as it can prevent you from inserting a shorted tube into your transmitter or amplifier, causing possible circuit damage.

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