Long Plate 12AX7, questions...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by JohnK24, Mar 2, 2005.

  1. JohnK24

    JohnK24 Supporting Member

    Dec 9, 2004
    North of Pittsburgh, PA
    Tonight I found an old Zenith 12Ax7 tube in my parts drawer. A friend gave me several older Zeith and Amperex 12AX7s and 12Au7s several years ago (most of the boxes were old, torn and only two are left, one Amperex, one Zenith). I tubed my former tweed Blues Jr. with the Amperex X7s and with a Weber C12NS that was a super sweet sounding amp (but I sold it for a Vox AC15). Fast foward to now...I've got a newer '03 Blues Jr. (w/ Alltone 1250) and it has had a whole set of JJ/Teslas (pre and power), but when I found this Zenith, I put it into the V1 slot...wow, the tone is detailed, but sweet and smooth...very nice with my strat, bluesy and fat, yet chimes and twangs on my tele.

    The Zenith definitely has "long plates" when compared to my JJs and Sovteks (stock tubes from the BJ). So...my questions:

    1. Do the long plate 12AX7s tend to have this warmer, rounder tone ?

    2. Anyone else see / use Zenith tubes ? Is this a rare guitar amp tube ?

    3. What are the "affordable" (less than $20/ea) long plate tubes...new or NOS ?

    I'm learning more than every about tubes and tone stacks these days...this website is a world of info.

    Thanks guys,

  2. saros141

    saros141 Guest

    Good to hear you found one you like for it... I had a Blues Jr. some time back and I wasn't crazy for the stock tubes.

    1. I've found that the length of the plate, as a variable taken alone, is not a reliable indicator of tone. There are bright longplates and warm, round 14mm-plate 12AX7s too.

    2. Is the tube you have really labeled Zeith or is it Zenith? If it's Zenith, I'd suspect an American manufacturer, like RCA, GE, Tung-Sol, or Raytheon. Are the plates black or grey? If you can post a picture we should be able figure it out.

    3. All of the above USA-made tubes should be findable (not necessarily new-in-the-box mind you) for under $20 apiece if you do a little hunting.
  3. JohnK24

    JohnK24 Supporting Member

    Dec 9, 2004
    North of Pittsburgh, PA
    Thanks for the reply. First off, it is a ZENITH (yeah, I misspelled it in the original post, edited it today).

    The plates are grey and double the length of those in my JJ Teslas.

    So, one of the other major US companies made these and Zenith just applies their label, eh ? The "e" and "n" of Zenith (in orange paint) are all that is left of the name. THe printing of the 12AX7 and Made in the U.S.A. is still very visable (grey paint) and is printed on the tube like this


    Anyhow, very cool tube.

  4. Blue Strat

    Blue Strat Member

    Aug 2, 2002
    Sterling, VA (not far from Washington DC)
    A photo would be the best way to identifiy the manufacturer.
  5. Wakarusa

    Wakarusa Member

    May 7, 2004
    Indianapolis, IN
    A current production 12AX7 with huge plates that also happens to sound really good in some amps is the Sovtek 12AX7LPS.

    Just don't use it in cathode follower circuits (i.e. to drive the tone stacks in old tweed Fenders and many Marshalls).
  6. Improviser

    Improviser Member

    Sep 2, 2003
    FWIW, I spoke to Lord Valve a few days ago and he advised that JJ were about to release a new long plate 12AX7. He's yet to try them out though.
  7. Jeff West

    Jeff West Member

    Mar 26, 2003
    Houston, TX
    John- I have actually seen 1958-59 mC6 Dutch Philips (Amperex) longplates rebranded by Zenith a few times. That's one of my favorite 12AX7s, so I kind of watch for those. But Zenith rebranded others more commonly. I think the "made in U.S.A." rules out the Philips. They would have seams on the top molded into the glass, and a distinctive "D" getter support ring with wider straight side of the "D" so they're pretty distinctive anyway.

    Although they could be by other makers, my guess based on your description viually and sonically would be Sylvania. Although photo would be more definitive, take a close look at one of the plates through the glass head on and if it is the Sylvania I'm thinking of, it will have two elongated staple holes on each side of the grey plate. But in addition, it will have two more similar rectangular hole/slits on the very outside of one side of the plate only, the other side won't have holes there. So one side of the plate has 4 rectangular holes total, the other has 2. There will also be a somewhat raised center section of the plate, and the copper support rods poking through the top mica will be perpendicular not parallel to the main plane of the plate. Halo at top, on one support rod.

    There are other possibilities, esp if the getter ring is angular not halo, but I'll hold it to that one for now!

    Glad you have one you especially like. You'll be checking old TVs put on the curb for pickup soon . .

    Jeff W.

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