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GE long plate 12AX7 differences.

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by rockon1, Aug 3, 2006.

  1. rockon1

    rockon1 Member

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    Ive noticed going thru my GE long grey plate collection that out of over 50 tubes 6 or so have slightly different plate construction.The one on the right side is the "oddball" and the one on the left seems much more common.[​IMG] Anybody shed some light on this? Thanks Bob
     
  2. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    That tube on the right definitely doesn't look like my long-plate GEs. I imagine it must have the GE "dots" on it, for you to call it a GE? Does it have the GE/KenRad EIA of 188-5? How 'bout that extra partial mica between the upper mica disk and the getter wire (can't see it on the left side one, but I assume it is on that one, as it is on mine)? Does it have seams on the top of the glass?

    How 'bout another picture of the upper part of the tube.

    - T
     
  3. Blue Strat

    Blue Strat Member

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    The one on the right is the only GE long plate type I can remember seeing.

    I'm 99% certain that the one on the left is something else. In general, GE 9 pin tubes have more points on the mica spacers than any other brand. Mica spacers are as good a "signature" as any to identify brands. Cutting mica, which is rock, is not trivial, and once they got their cutting tools worked out, they generally didn't change them.

    Hey TW, aren't you on vacation? ;)

    PS, the one on the left looks more like an RCA. Is the "12AX7" etching near the top and enclosed in a rectangle (actually, an "flattened" octagon)?
     
  4. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Yeah, but I couldn't resist dropping by, just so I could put a kink in your tetrode. :rotflmao :crazy

    - T
     
  5. rockon1

    rockon1 Member

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    They both sport the typical GE
    12
    AX7
    ...
    .
    type etchings. I looked at more of them and interestingl enough most of the type on the left has the more typical pointly mica spacers you speak of. They all have destinctive GE ecthings though. I have a lot more of the type on the left so I thought they were the more common of the two!
     
  6. rockon1

    rockon1 Member

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    Yes it does have the typical GE etchings(with dots). Ive noticed other slight variations that mike pointed out with the mica spacers however I have others that have more typical mica with the same style plates as the one on the left. I will try to get some more pics later. thanks Bob
     
  7. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I'll have to look at mine, as well, but I'm away from my stash. Those notched micas seem unique, and vaguely familiar, but I just can't place them off the top of my head.

    - T
     
  8. rockon1

    rockon1 Member

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    OK heres a pic of another GE branded,GE etching with more familiar GE mica. [​IMG]
     
  9. rockon1

    rockon1 Member

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    [​IMG]Heres another with mica like the first. Confusing isnt it?
     
  10. rockon1

    rockon1 Member

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    BTW-Timbre Wolf-You say the one on the right doenst look like the GE's youve seen. Blue Strat says the one on the right is the only one he remembers seeing. At first I thought you both were in agreement.
     
  11. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    And I almost submitted my first reply with the left-right mistakenly switched. I'll have to double-check my stash when I can, but I think the non-notched mica version (left) is more common for me.

    - T
     
  12. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    All right, I just checked my long-plate GEs. They're all etched with the "stencil" 12AX7 and dots. The plates all look like the one on the right (with notched mica disk), not the one on the left - so I was wrong about that. For me, the more common form is the circular mica disk (these all labeled "Baldwin," not the notched one.

    Here's the key difference, though: the notched-mica versions are printed "6681" (=low noise 12AX7, as tested by GE, before labeling). Printing for the 6681 is in red, and the brand is "GE" (with logo).

    My take is that GE made both circular and notched-mica disk versions. Perhaps Mike has only seen the notched variety. They (GE) likely issued the notched ones as plain 12AX7, as well as selected ones as 6681.

    What I don't know about is the tube you have on the left - the plates are different. Look at the "ladder" part (especially the vertical sides of the "ladder"), plus see how the plate-fastening tabs fold in on the left example, and out on the right example. Looks like you've got a third version of a long-plate GE there, Bob. Does it have two small holes on the thin edge of each plate, like the one one the right does?


    - T
     
  13. rockon1

    rockon1 Member

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    I have plenty of both types of plate design . Probably since I own about 50 -60 of these GE long plates. Also the plate fastening tabs arent that consistent either. On one tube I looked at they folded in on one side and out on the other ,on another both in and on another both out! Also if you look at the latest pics I posted those only have one hole fastening design....... Some have one hole in thin edge of each plate some have none! A lot of slight variations !
     
  14. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Different manufacturing batches? I'll bet the changes could be tracked by date.

    - T
     
  15. rockon1

    rockon1 Member

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    Yeah,me too. Unfortunately aside from the etching many have little else to go on. I was hoping to pick up some info here. As I am curious I may have to unbox all of mine and search for more info !
     
  16. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Normally the Tubemonger tube picture library is helpful for these kind of things, but I don't see any long-plate GEs there.

    - T
     
  17. rockon1

    rockon1 Member

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    Ok Ive been busy with other things however Ive got a date code of 57-43 188-4 on one thats got single plate fastening hole and plates that are ribbed down the side like tube ON THE LEFT in picture. Got a date code of 60-48 188-5 for one that has plates like one on right[​IMG](but more standard mica without notches) in (no ribbing down the sides)
     
  18. rockon1

    rockon1 Member

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    Went thru my entire GE lp collection.Heres an interesting one. Actually I found 4 like thisThe date code reads 2-09 188-5 Could that be 1952? its not missiing the first digit. Ive got others that say 57,58,etc. At any rate its got a horseshoe getter,copper rods and no extra mica piece on top.[​IMG]
     
  19. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    My non-notched mica 12AX7s have a horseshoe getter, and the plate "ladder" has no raised vertical edges (like your photo on the right). They're from the "188-20" plant (don't know where that was), in 1959.

    My "6681" (etched "12AX7") have halo-getters, and also the same style "ladder" on the plates (no raised vertical edges). They're from the Owensboro factory, with code "188-5" and they have notched mica disks.

    Upon closer inspection, it seems the direction of plate tab folding is random on all my "GE" samples.

    Older 12AX7 from Owensboro/188-5 ("KenRad" labeled) from the early '50s (most of mine from '51) have silvery black plates, and non-notched mica disks. Their plate structure is more like the photo on the left, above, (have raised vertical edge "ladders"), but they've got one plate fastening hole instead of two.

    Clearly there were lots of changes to their manufacturing process over time, but different plants probably had different mica and plate styles being used at the same time, too.

    All of these tubes sound fantastic, by the way (though the KenRad black-plate is quite different from the long-plate GE), and that's the only real reason to care so much!! :BluesBros

    - T
     
  20. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I'd expect that to be 1952, because my '51 KenRads also only have one digit ("1"). That photo shows plates that look just like my KenRads, except that the KenRads have the silvery-black plates. Same Owensboro plant EIA code of 188-5.

    - T
     

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