More Tube Identifications

Discussion in 'Amps and Cabs' started by danieldroukas, Jun 19, 2006.


  1. danieldroukas

    danieldroukas Member

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    I have a slew of old tubes laying around the house that I've gathered up from multiple yard sales and thrift markets. Here are just a few I'm curious about:

    #1: 12AX7 labeled Webcor and Made in Great Britain. Has four creases in the dome of the tube.

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    #2: Webcor 12AX7 with 12AX7 in octagonal logo. Smoking on side of glass.

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    #3: 12AX7 that came in an RCA box. May not be the original box.

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    #4: 6BQ5/EL84... black plates... Mytron labeled.

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    #5: Motorola labeled 5881. Red base.

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  2. danieldroukas

    danieldroukas Member

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    LAST ONE... I think this is an RCA black plate 6L6... but I wasn't sure if the vacuum has been broken since the smoking has turned somewhat white...

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  3. drbob1

    drbob1 Silver Supporting Member

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    That last one is dead, sorry.
     
  4. danieldroukas

    danieldroukas Member

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    any ideas about the first 5?
     
  5. Tread

    Tread Member

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    Well... the 6BQ5/EL84 looks very much like a Quad of them I got out of a Late 50's RCA Victor Phono/Stereo last week...Black plates that wrap around the tube...round halo getter but mine say RCA on them.....
    Haven't tried them yet...gotta test'em first.
     
  6. Blue Strat

    Blue Strat Member

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    #1 is a Mullard 1950s "long plate" ECC83
    #2 is a (probably 50s) RCA clear top 12AX7
    #3 Not sure, need more photos...could be an RCA blackplate 12AX7
     
  7. danieldroukas

    danieldroukas Member

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    Here are more photos of unknown #3. It came in an RCA box... but I'm not sure if it's the original box.

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  8. Tread

    Tread Member

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    Thats an RCA 7025
     
  9. Blue Strat

    Blue Strat Member

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    With 12AX7 etched in the glass?

    It's a blackplate RCA. Note that the RCAs ALL have the tube number etched inside a rectangle, actually, a flattened octagon. Larger RCA tubes have a normal looking octagon.
     
  10. Tread

    Tread Member

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    OOps missed that one...looks just like an RCA 7025 I'm lookin at right now....xcept this one's a grey.
     
  11. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Confirm this with the etch codes: near the bottom of the tube, there are two lines of letters/numbers. The second line should start with "B" for Mullard's Blackburn factory. The first line will be "mC1" for square-getter, or "f91" or "f92" for circular-getter.



    The 6BQ5 looks just like a Sylvania black-plate to me - I like those a lot. RCA black-plate 6BQ5 don't have the ridges in the rounded part of the plate, have a flatter flat side, and less-reflective black. I like RCA black-plates a lot, too.

    The 5881 has GE's EIA code ("188") on the base. Hmm....

    - T
     
  12. Sparky6string

    Sparky6string Member

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    I saw the base and thought Tung Sol, but with the "Canada" on the side perhaps Marconi?
     
  13. Blue Strat

    Blue Strat Member

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    Apparently, GE did tube production in Canada as well as the US>
     
  14. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    That 5881 definitely is not a Tung Sol - the insides look different. Looks like Motorola contracted with GE to make those, but GE may have bought them from a Canadian company (Marconi? Westinghouse?). I don't know the location of the GE factory with the 188-20 code, but I think it would have been inside the USA - which means you can't rely on the printing, even if it is coded. You've got to go to the guts of the tube.

    - T
     
  15. danieldroukas

    danieldroukas Member

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    are the four creases on the top of the glass of a tube indicative of a Mullard manufactured tube, or am I wrong to assume such? I'm looking at the tube I was told was a mullard, one that is labeled a mullard 12AX7, and two Amperex tubes that all have the four creases on the dome of the glass. Are Amperex tubes made by mullard?

    Oh, and is there any way I can tell what member of the 12A family a tube is? I have a few tubes that have just the ECC but the ending has been rubbed off.
     
  16. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I think the seams on top of the tube are indicative of the Philips conglomerate of tube manufacturers, but that is a broad group (Mullard, Philips Miniwatt, Amperex, Valvo, BEL, POPE, Matsushita, Siemens & Halske, even older Ei!! I'm sure I left out some). To really identify tubes made by Mullard, you've got to go to the etch codes. Here's another page with more thorough information on Philips etch codes.

    I would also recommend using the etch code (if it is available) to determine which 12A_7 tube you've got. The first line of the Philips code tells the tube type. You can get the list of type codes from Brent Jesse's informative site (same link as above). I don't recommend trying to just look at the inside of the tube (at construction: plates, etc.) because some ECC82/12AU7 look exactly like ECC83/12AX7. Of course, if you think you've got one or the other of the 12AU7/12AX7, you can plug in to a 12AX7 slot (not a 12AU7 slot) in an amp and confirm by the response. If all you know is that its a 9-pin tube, of the same 12AX7 dimensions, don't plug in to your amp until you know what it truly is.

    - T
     
  17. Blue Strat

    Blue Strat Member

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    4 seams in an X pattern is more indicative of Philips on "the continent" and 2 seams in a straight line is more indicative of Mullard Blackburn UK.

    Of course, etched production codes are more concise and always appear on Philips tubes.
     
  18. danieldroukas

    danieldroukas Member

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    OK... so I have an Amperex ECC83. I believe it reads I6(6 or 5) then below it reads (delta)1J2. There is also the 3 digit screen-lettered code 222 on the exact opposite side of the tube.
     
  19. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I65, plus the delta (for Heerlen, Holland factory) equals Amperex or Philips Miniwatt (they were branded both).

    - T
     
  20. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    The # of seams isn't indicative of either manufacturer. As Mike says, below, go with the etched codes for that information.

    I finally got around to double-checking your statement, Mike, because I didn't think it was consistently true. Sure enough, the older ('50s) Mullard long-plate 12AX7 (Blackburn) has four seams on the top. Later-production, short-plate Mullard 12AX7A only have two seams (as do Mullard's '60s and '70s Blackburn-made EL84 and Mitcham-made 12AT7, from '60s-'80s). Amperex tubes seem to all have four seams, but so do other tubes from the Philips group (Miniwatt, Matsushita, Valvo, Ei).

    For identifying the factory origin, I agree with your second statement on referring to the etched codes - they're more reliable.

    - T
     

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