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help with tube identification

Discussion in 'Glowing Bottle Tube Amp Forum' started by rosa, Oct 23, 2020.

  1. rosa

    rosa TDPRI Member

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    Hello,

    I have nice small guitar amp i modified from a film editing system amplifier, and it has the pictured tubes, a 12ax7 and a 6aq5a. They work fine as of now, but I would like to get replacements, for when they fail, as similar as possible, without getting into expensive NOS.
    i really like the tone it has, but i am unsure if it has more to do with the speaker i am using or the specific tubes.

    is it possible, by looking at these photos, to narrow the options down?
     

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  2. TwoBear

    TwoBear Tele-Meister

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    You shouldn't have any problem finding substitutes I guess I'm going to assume that you're trying to get as close to those same tubes as possible, and if so have you tried looking at them closely with different angles and light shining on them possibly a Jeweler's loop to see if there's any markings that may have been there that have rubbed off also underneath the tube let's see what's under there that may help you if you are indeed trying to find exactly what maker that was or brand or whatever... Again assuming that there's no other markings that you've seen but may be there. And just for the heck of it what speaker are you playing it through, there's all kinds of little film projector amps that actually sound great for guitar. The a at the end of 6aq5 I think denotes a slow start heater (if so you should probably stick with the same type) and that might account for the fact that you don't have a tube rectifier, and that would have to be a certain type also to be a slow start... I'm sure others will chime in with better information than I've got but the preamp tube the 12ax7 is maybe one of the most mass-produced. The one you've got there looks like it's got nice large gray plates and the pins don't look like they're all discolored. I apologize if I'm telling you stuff that you already knew.
     
    Last edited: Oct 23, 2020
  3. Peegoo

    Peegoo Poster Extraordinaire

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    That 6AQ5A power tube is a beam tetrode, also known as an EL90 and CV1862. The one you have was made by CEI.

    The 12AX7...hard to tell the brand from that one pic. Possibly Hytron, Brimar, or Telefunken. Try breathing some fog onto the surface and look quickly under a bright light for remnants of other printing on the glass. Another trick is to shine a UV light on the glass, which sometimes reveals markings not visible in regular light.
     
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  4. rosa

    rosa TDPRI Member

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    ok thanks, Ill take another look in sunlight. the speaker is a Jensen p12rj. And the amp does use a rectifier tube, a TUNG-SOL 6X5GT.
     
  5. TwoBear

    TwoBear Tele-Meister

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    Yeah I got off my phone and looked at it on the computer and I saw the CEI on the power tube I think it was a wholesaler possibly based in England that rebranded so yeah it's a good chance that it was a high quality or both were high quality tubes to begin with. Does the amp take a inordinately long time to heat up, to come to life so to speak. I'm guessing 15 seconds for the tubes to warm up, you could look up specs and see. But if it's sounding good and doesn't take forever to give up the goods then they're probably still fine. What about the electrolytics? When you say you got it up and running did you change those out because that looks like an oldie and yeah I guess they haven't made that stuff for a while so that's pretty obvious haha. Again the slow startup characteristic of that beam tetrode may have been helping to not slam the power section. Anyways good luck.
     
  6. rosa

    rosa TDPRI Member

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    it powers up fairly quickly. 10 seconds or so. I changed all the capacitors when I got it running. the reason Id like to have a similar backup set is because I plan on traveling abroad with the amp to a place where there are less options available than in the US.
     
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  7. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    I'd have to know more about the circuit to say for sure, but I think any 12AX7, 6AQ5, and 6X5 you can lay hands on should keep you going just fine. About $35 for the set at AES, and that's for NOS/new tubes. :)
     
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  8. ArcticWhite

    ArcticWhite Tele-Afflicted

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    Vintage 12ax7s with long grey plates are all over eBay for 15 or 20 bucks.
    But the one you have will probably be good for another 20 years.

    That's a really cool looking amp too.
    Would love to see some pics, inside and out.
     
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  9. tubegeek

    tubegeek Friend of Leo's

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    Is that amp pulled out of a Steenbeck? That would be SO cool. I learned to use a Steenbeck about 30 years ago, what a beautiful machine.
     
  10. rosa

    rosa TDPRI Member

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    Ive been trying to find out where it came from, but cant find any references to it. There is much more information about the moviola amps on the internet, and that helped me fix this one. I basically bypassed a second preamp tube, swaped the tape head to a 1/4" jack input, and changed some resistor and capacitor values, trying to get as close as possible to a fender champ. Also got it a bigger output transformer. I really like how it sounds with a larger speaker. Ive ordered a set of nos RCA power and rectifier, and a Sovtek 12ax7lps
     

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  11. tubegeek

    tubegeek Friend of Leo's

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    Kool Konversion!
     
  12. MuddyWolf

    MuddyWolf Tele-Meister

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    I can confirm the identification. That is a tube. And a very tubey tube by the looks of it. But it might be a valve. A valvey valve. So its either a tubey tube or a valvey valve. For sure.
     
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  13. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    I very nearly misidentified them as valvey tubes. Glad I held my tongue on that part! ;)
     
  14. Paulie Walnuts

    Paulie Walnuts Tele-Meister

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    The 12AX7 tube is a I63 series Mullard 14mm short plate. And a nice desirable tube easily replaced with another at anytime
     
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  15. JWH7

    JWH7 TDPRI Member

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    The 12ax7 looks american made. GE more than RCA. thru the years all tube manufacture made little changes to the plates mica getters so its an alien tube from outer space if you want it to be
     
  16. blues

    blues Tele-Holic Silver Supporter

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    It's a Mullard. I can see numbers etched into the glass. If there is a B its from the Blackburn plant.
     
  17. Intubator

    Intubator Tele-Holic

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    If it were a Telefunken it would have a diamond etched/molded in the bottom of the glass between the pins. Some Telefunken's were rebranded euro tubes so its worth a look. They are considered some of the best made.
     
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