Blackburn/Mullard EL34

Discussion in 'The Workbench' started by StingRay85, Apr 13, 2021.

  1. Dblgun

    Dblgun Well-Known Member

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    Thanks for the information it is very interesting and useful for a great number of folks. Looks like these GE's are XF2 single halo from 1970.
     

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  2. StingRay85

    StingRay85 Well-Known Member

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    Yeah I would never spent money on these kind of tubes. When the getter flash looks like that, they have been extensively used. Also, they are not really well matched. But they do indeed measure in an acceptable region. I have 15-20 tubes like this, but it seems outrageous to ask 150 a piece when they are approaching end of life.

    Also be aware that Maxi Matcher 2 measures and compares current at 400V -36V bias, but its not always a guarentee that at e.g. 450V the matching is still sufficient .
     
    Last edited: Aug 4, 2021
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  3. StingRay85

    StingRay85 Well-Known Member

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    Indeed, they do appear to be new or only slighty used. Very nice. Are they yours?
     
  4. Dblgun

    Dblgun Well-Known Member

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    Yes, I got these and some 6550's from the family of a gentleman who seemed fond of GE's.
     
  5. StingRay85

    StingRay85 Well-Known Member

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    Now with better light on my phone I can clearly see that the tubes are in fact unused or "new in box". The dark edge around the flash is clearly visible. These are the real gems
     
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  6. StingRay85

    StingRay85 Well-Known Member

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    EL34.jpg
    Some more test data of my tubes. Current draw really doesn't say much about the quality or lifetime of the tube. I would say an arbitrary value of 25 mA is where I would start selecting for my own amps.

    Also, when comparing this to RFT, you can clearly see that transconductance is significantly lower on these tubes.
     
  7. StingRay85

    StingRay85 Well-Known Member

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    20211025_164921_copy_774x1032.jpg

    20211025_164950_copy_774x1032.jpg

    20211025_164848_copy_774x1032.jpg

    This is what ANOS (almost new old stock) looks like. The thin silvery flash layer is turned brown. I guess somewhere between 10 and 100 hours on it
     
    Last edited: Oct 25, 2021
  8. Fernieite

    Fernieite Member

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    What a fantastic thread! I just joined the forum because of it! :applause:

    I've got a pair of Rogers labeled Blackburn xf2s from 1968 that need to be replaced.
    Can anyone help me find a decent matched pair? (feel free to pm me)

    blackburn 1.jpg blackburn 2.jpg
     
    Last edited: Oct 29, 2021
  9. VladSRB

    VladSRB Member

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    Have two NOS pairs like this, branded Giant Electronic Brand xf3 tubes (not selling)
    Its getting harder and harder to source them in good condition for reasonable price. Mullard made EL34s are top notch. Great idea to make a thread about them.
     

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  10. StingRay85

    StingRay85 Well-Known Member

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    Surely not the freshest looking tubes, but i've seen worse Xf2. I would guess they don't match anymore, and thats why you want to replace?
     
  11. Fernieite

    Fernieite Member

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    No, unfortunately one of them is dead now. :(
    The other one (Pictured) still tests strong on my tech's tester, but I can see slight rainbow colors below the flash line. It's on it's way out I'm afraid.
     
  12. StingRay85

    StingRay85 Well-Known Member

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    Too bad, they're not cheap to replace
     
  13. Pete Farrington

    Pete Farrington Well-Known Member

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    Provided there’s plenty of good getter flashing remaining, that doesn’t concern me. I take a bit of rainbow to indicate that at some point, the valve may have been overheating a bit in use. So check everything is ok. As long as it performs as it should, puts out good signal power, no big deal, carry on enjoying it.
     
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  14. Fernieite

    Fernieite Member

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    Good point man. The remaining working EL34 is still usable, but I'd still like a somewhat better matching pair to use primarily. This old one will be a spare.
     
  15. Matthews Guitars

    Matthews Guitars Well-Known Member

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    A little bit of rainbow doesn't mean there isn't a lot of life left in the tube.

    I was going to say something about getter chemistry but I think I already did that on page 2.
     
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  16. StingRay85

    StingRay85 Well-Known Member

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    But if one out of two is dead, he needs a new pair. The one that's still alive has a bit of value left. Try trading it with someone for a fresh pair of EH?
     
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