Help putting in preamp tubes!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by atomheartmother, Jan 4, 2005.


  1. atomheartmother

    atomheartmother Senior Member

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    Location:
    La Crosse, WI
    Amp: Echo Twin 45 (60's clone of a Super Reverb)

    Tube numbers are written next to the sockets.
    From left to right (starting next to the powertube):

    12AT7
    6AQ8
    12AX7
    12AX7 (I think)
    12AX7


    These are the tubes I have:

    Ruby 12AX7
    Svetlana (I don't know what it is...the rest is worn off)
    Unmarked tube
    RCA ECC85/6AQ8
    JAN Phillips 5814A (12AU7?)

    I also have a JJ ECC83S that I'm going to use in the first 12AX7 socket (all the way to the right).

    The owner told me that the socket next to the power tube is the phase inverter and you should use a 12AT7. I don't know which tube is a 12AT7 though. The socket next to that is for the reverb/trem...he said I should use a 12AU7 (this socket has 6AQ8 written next to it).

    I've noticed that the JJ ECC83S, the Ruby, and the unmarked ones are all the same size and bigger than the Svetlana, RCA, and JAN. Are 12AX7's physically larger than lower gain tubes, or does actual tube size just vary by manufactuer?

    Any other input?

    Also, the voltage switch on the amp has an option of 100 volts or 117 volts. Which one should I use?
     
  2. saros141

    saros141 Guest

    Sounds like a modded clone to me... neither the blackface nor the silverface Super Reverb originally came with an ECC85/6AQ8 (a tube that's usually used in radios, it's also a dual triode but the pinout is slightly different from the 12A_7 types). And the guy says to put a 12AU7 in that socket? I'm as confused as you.

    BTW 117 is the voltage setting you want for N. America... in all respect, since you asked that... I'd say the safest thing to do is just take it to a good tech as there might be other things boogered with it.
     
  3. atomheartmother

    atomheartmother Senior Member

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    What's the worst that could happen if I don't have the "correct" tubes in the "correct" sockets? Nothing could be damaged, right? I'm just not sure if there's much they could do short of replacing the tubes, and I'm pretty short on cash now as it is.
     
  4. saros141

    saros141 Guest

    Well, on an ECC85, pin 9 is connected to a shield between the triodes... on a 12AU7, pin 9 is the center tap for the heater filament. So, if the matchup is wrong, you might get a loud hum or it might not work at all, with slight possibility of damage to the tube itself... I highly doubt it would hurt anything else in the amp.

    I'm not an experienced tech, though. Our esteemed Mr. John Phillips, who's probably asleep over in Scotland right now, could likely give you a better answer, good chance he'll look into this thread the next time he logs on!
     
  5. atomheartmother

    atomheartmother Senior Member

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    What is an ECC85? I know an ECC83 is a 12AX7, ECC82 a 12AU7?, etc. Would an ECC85 have more gain? It seems as the number after ECC gets lower, so does the gain.


    Also the only reason I'm thinking of putting the 6AQ8/ECC85 tube in the spot is because the socket has 6AQ8 written next to it. Does a 12AU7 belong in this spot? The Jan Philips 5814A is essentially a 12AU7, I believe. Or at least that is what I read somewhere.
     
  6. John Phillips

    John Phillips Member

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    I don't know anything about that amp - although if the tube information is correct, it's not a clone of a Super Reverb, or any Fender. It may be a similar amp, but in that case all bets are off regarding tubes.

    Are the tube markings on the amp original? Or just penciled on by a previous owner/tech? Could it have been modified?

    If you're sure the 6AQ8 marking is correct, use that one there. As Saros says this is not interchangeable with a 12AU7, so unless you know that the marking is wrong and the previous owner is right, don't use one.

    You can usually interchange the other types (12AX7, 12AT7, 12AU7) without doing any harm, although the amp might not sound at its best.

    Set the voltage to 117.
     
  7. TheAmpNerd

    TheAmpNerd Member

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    What John and Soros said.

    Additionally, I would go out and buy some known good
    tubes.

    Talk to the old owner and get some as much information from him about the amp too. That won't hurt but could
    be the blind leading the blind.

    This could be a one channel verson that <insertnamehere>
    decided to make of a super reverb.

    Typically the phase inverter is closest to the
    power tubes, but not all amp are logical either.

    See if you can't scrounge the net for a schematic.

    Good luck and keep us posted.
     
  8. atomheartmother

    atomheartmother Senior Member

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    Thanks for the help. I really didn't give you guys much to work with. There is absolutely nothing about this amp on the internet. The previous owner didn't know much either. He said that he'd "traced" the circuitry of the amp once and it looked exactly like a Super Reverb...whatever. I really don't care. He said that he didn't know much about the tubes in it and that he just had a tech put in new tubes a year ago or something.

    The tube markings look like they were penciled in. There is no schematic anywhere.

    The second preamp tube socket from the left does have 6AQ8 written by it, so I guess I'll use it there. The tube came with the amp, so I imagine that is what socket it was in.

    The rest really don't matter so much, do they? The places where the tubes are may affect the tone, but won't hurt anything, right?

    I'll probably just take it into a tech and do a full retube sometime. However, that'd cost probably $100 with a bias, and I honestly have no extra cash at the moment because of X-Mas and all.

    I'll just have to see what happens...
     
  9. atomheartmother

    atomheartmother Senior Member

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    Does physical tube size (size of glass enclosure) have anything to do with the type of tube it is? I've noticed that the JJ ECC83S, the Ruby, and the unmarked ones are all the same size and bigger than the Svetlana, RCA, and JAN (as well as a JAN GE 5751 I have in another amp). Are 12AX7's physically larger than lower gain tubes, or does actual tube size just vary by manufactuer?
     
  10. Lonely Raven

    Lonely Raven Member

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    No, different manufacturers just use different envelopes.
     
  11. saros141

    saros141 Guest

    The size (height) of the plate stuctures inside can give you a clue sometimes, which might help you ID your unlabelled ones... 12AT7 types usually have very short plates, often with a flange on only one side.

    Only one 12AX7 type I can think of (RFT) strongly resembles a 12AT7, most of the other ones have taller, wider plates with the familiar ladder/waffle pattern.

    Unmarked 12AU7s and 12AX7s are difficult to distinguish from each other... maddeningly, as anyone who's sifted through piles of old tubes knows, the 7AU7 looks the same too. (YAY! I just found an RCA blackplate... 7AU7 :( )

    Good luck ahm!
     
  12. atomheartmother

    atomheartmother Senior Member

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    Wow. That was weired. I tried it out...doesn't sound good. I'll have to take it to a tech. The volume kept cutting in and out, the reverb sounded weird, there was loud popping and crackling, and the tone was kind of super bright and and no bass...

    Besides that it sounded pretty good though. Here I come with more crap for you to fix Dave's...I've been there twice getting stuff fixed in the past 2 weeks...

    Do they have tools or anything that can tell what type of tube needs to go in which socket?
     
  13. drbob1

    drbob1 Silver Supporting Member

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    Those are not the sounds of a tube in the wrong socket likely. Those could be: bad caps, cold solder joints, dirty contacts, bad transformers, bad tubes and a host of other problems. A good tech should be able to sort it out, although it'd be easiest if you have a good 6AQ8 and it's in the right place...
     

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