"what tube is this" volume 9765432

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by brad347, Aug 3, 2006.


  1. brad347

    brad347 Member

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    I don't usually post these games but what the hell! I have a couple of mystery tubes that I harvested from a thrift-store-find tube 2-track by webcor. Already got a pair of Mullard EL-84s, two Mullard 12AX7s, and two Mullard 12AU7s out of it, so totally worth the 20 bucks I paid! :D

    But I went digging around in there tonight and grabbed the last 2 tubes out... these Webcor branded tubes that say "made in USA" and are obviously not Mullard. All other tubes in here were mullard and all are branded Webcor so appear stock... this seems odd to me why they would choose a different, USA brand for this pair of tubes. They have the "A" suffix so maybe that has something to do with it. At any rate, WHAT ARE THEY? I think I took some good pix. Haven't tried them in anything, not too curious really, just idly curious. Have a look!

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  2. brad347

    brad347 Member

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    not necessarily true. 12AX7As are premium 12AX7s that are selected out for low noise. At least that's what I was always told.
     
  3. Jack Briggs

    Jack Briggs Member

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    .......what he said!
     
  4. brad347

    brad347 Member

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    well what do you mean by "old days."

    this 2-track is from the 60s so I would assume that these tubes qualify. I did know about the spiral-wound filaments. But your original post was misleading unless I am mis-informed... does the ECC-83 have spiral wound filaments?
     
  5. mc5nrg

    mc5nrg Supporting Member

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    I thought the A suffix haqd something to do with whether the tubes could be used in a series string circuit (or maybe the opposite) like in certain televisions?
     
  6. AdmiralB

    AdmiralB Silver Supporting Member

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    Those are Sylvanias, FWIW.
     
  7. brad347

    brad347 Member

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    Ah, makes sense. Thanks!
     
  8. rockon1

    rockon1 Member

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    One of my favorites. Kind of a "dark horse" so to speak but I really like those short plate/square getter Sylvanias. Kind of a smooth/rolled off top end with a nice mid kick. I find them nice for fattening things up with a bright amp. Might make a mid heavy set up muddy though.
     
  9. brad347

    brad347 Member

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    thanks rockon1. Good to have a pair in the arsenal, I guess... maybe I'll put one in the bass amp, which is an ampeg B-25B. That damn thing is way too bright for its own good.
     
  10. drbob1

    drbob1 Silver Supporting Member

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    There's a really cool web page that goes thru the advertising for tubes from the 30s on up, pointing out the little inconsistencies. Anyway, it seems very unlikely that tube manufacturers actually hand selected better tubes for the 7025 or 12AX7A label. It seems likely that after the late 50s when the 7025 label came out that all 12AX7 tubes were designed and built the same. So, deep breath, those are basically the same as any other 12AX7 tube by the same manufacturer. Why are they different? Perhaps the original pair were bad and replaced early in the recorders life? Anyway, nice score for your stash!
     
  11. Blue Strat

    Blue Strat Member

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    I'm almost certain they're not. My guess is Westinghouse based on the typeface of the etching. Sylvanias are much more common and very easy to spot.
     
  12. brad347

    brad347 Member

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    Thanks for the insight drbob1. However, one inconsistency remains... on the tube chart for the recorder, those two spots are specified as 12AX7A and the other 12AX7 spots just say 12AX7. Any idea why?
     
  13. brad347

    brad347 Member

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    WHOA, an interesting twist to the story! ;)
     
  14. Blue Strat

    Blue Strat Member

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    The "A" sockets are probably higher gain stages which are more susceptible to noisy and microphonic tubes much like the 7025, versus 12AX7, sockets in Fender amps.
     
  15. AdmiralB

    AdmiralB Silver Supporting Member

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    You're right - the plate structure looks proper but the getter is wrong.
     
  16. Blue Strat

    Blue Strat Member

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    I've never seen a Sylvania plate that looks like that. It resembles a post 1960 GE more than any Sylvania I've seen.
     
  17. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I'll back Rockon up on this, since he turned me on to them (thanks Bob!) - his description of their character is right-on.

    Sorry to break it to you, Mike, but those are definitely Sylvanias, though you're excused (partially ;)) because they're not very common. The plate structure/shape looks like an old, American 5751, but if you look at long-plate (gray plate) Sylvania 12AX7, you'll see similar shape, but just taller. Square-getter, made from about '56-'58.

    I like 'em, and find them to be sorta, kinda akin to the RFT ECC83, what with their breakup characteristics, but they've got more clarity than the RFT.

    - T
     
  18. Blue Strat

    Blue Strat Member

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    Count the points on the mica spacers. This means much more than a getter shape ;)
     
  19. brad347

    brad347 Member

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    LET THE RECORD SHOW:

    12 points on these mica spacers. YOU MAKE THE CALL!
     
  20. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Don't know about the fine points of which you speak, Mike, but I've got one that looks exatly the same inside, right in front of me. It is labeled "Magnavox", but it has Sylvania's EIA code (312), and it was made in '58. Same plate structure, same getter wire, same mica shape (points and all), same plate tabs, etc.

    I stick with my i.d. of Sylvania. But what do I know??

    - T
     

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