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Name this guitar tube amp component, and do I need it?

Discussion in 'General Electronics Discussion' started by dietermoreno, Mar 5, 2013.

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  1. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    I have a 100 watt Peavy tube guitar amp.

    Inside from the back it looks like this from left to right:

    power supply transformer > tubes > empty slots > output transformer



    The empty slots are labeled "12AX7/ECC83", without the quotation marks.

    The empty slots look like they are sockets for tubes.

    What exactly would tubes do after the power gain section?

    Isn't the pre amp gain section before the power gain section?

    Do power gain sections and pre amp gain sections use different tubes?

    All of the tubes that are currently in place are labeled as "EL34", without the quotation marks.

    Am I missing out on anything with my guitar amp not having the 12AX7/ECC83 tubes?

    It sounds too distorted for my liking and I prefer to use a distortion pedal with a solid state Marshal MG15 amp, as distortion is the nature of tube amps, but I was curious anyway on how that piece of junk sitting in my corner works.
     
  2. shrtrnd

    shrtrnd

    3,821
    519
    Jan 15, 2010
    You may get some info from someone else on this site that knows more about guitar amps. I've never seen a piece of gear with tube sockets that weren't used. If a socket is there,
    a tube probably ought to be in it.
    12AX7 is the U.S. equivalent of the British ECC83. Either tube will work.
    The EL34 is also a British tube designation (the British call vacuum tubes, 'valves')
    Maybe somebody else will come on here with any additional info.
     
  3. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    The ECC83 is a dual triode amplifier and I would expect it to be in the preamp or tone control stage. I cannot understand how the amp can work without it unless there has been a bodge.

    The EL34 is a power output valve, often used in pairs. Two can give 30W with no problem. How many have you got?

    It may be possible to get some idea of the circuit from pictures above and below chassis.
     
  4. john monks

    john monks

    693
    2
    Mar 9, 2012
    Tubes do nothing after the power gain section.
    The pre amp gain section comes before the power gain section.
    The power gain section typically uses a EL34 or EL84 or some similar tube. Most often a beam power tetrode. The pre amp section typically used a 12AX7 or similar triode or dual triode. This is a voltage amplifier.
    Without all the tubes I suspect the amplifier will not work.
     
  5. GonzoEngineer

    GonzoEngineer

    321
    2
    Dec 2, 2011
    If there are empty tube sockets, my first guess is that someone mucked it up with some modifications to the original. What is the Model Number for your Amp?
    Schematics are pretty easy to find on the internet.
     
  6. shrtrnd

    shrtrnd

    3,821
    519
    Jan 15, 2010
    Yes, come to think of it, I've seen some old tube amps with some of the unit converted
    to solid-state (by a 'mucker', as noted by GonzoEngineer). You might want to look
    under the chassis, and see if anybody added any additional parts to replace the old
    12AX7's, before replacing them in the sockets.
     
  7. GonzoEngineer

    GonzoEngineer

    321
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    Dec 2, 2011
    Hey Shrtrnd.....were you in Artillery?
     
  8. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    Some sharp and well lit pics of the upp and lower sides of the chassis wouldnt go amiss either

    please provide :)

    Dave
     
  9. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    There are 4 ELL34's in the power gain section.

    There are empty sockets for AX712's in the pre amp gain section.

    So you suppose that the amp has been modded by the previous owner to make the pre amp gain section solid state?

    The amp patent number is 5, 197, 102.

    The amp doesn't have a model number printed on it. I bought it used from a friend so I don't know any thing about it that isn't printed on it or I couldn't figure out by experimentation.

    The brand is Peavy.

    The make is Windsor.

    The wattage is 100W.

    I don't know if 10kbyte cell phone pictures will do any good. I don't have a real camera. I have a Flip video camera, but it sucks too and is only slightly better than my cell phone camera.

    When you say "look under the chassis", what exactly is "the chassis"?

    Is the chassis the part that holds the power tubes, pre amp tubes, power supply transformer, and output transformer? You know, the part that is accessed by unscrewing the screws on a grate?
     
    Last edited: Mar 5, 2013
  10. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    the chassis ---- the metal frame that the tubes and transformers etc are mounted on

    surely your phone cam is a at least 5mpix most are that or more these days.
    get the unit into good light, take pics resize them to a max of 800x600 and ~ 100kb

    too easy
     
  11. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    Oh, so you want me to look under there to see the circuit skematic.

    It looks like the chassis is bolted on and underneath the chassis can be accessed by loosening the bolts.

    This is so much easier than looking at the circuit in my Marshal MG15 that is solid state. My MG doesn't even have a chassis, or at least I have no clue where to find it because there isn't a huge grate for me to look through.

    I'll get on that eventually after I find the correct wrench to loosen the bolts.
     
  12. shrtrnd

    shrtrnd

    3,821
    519
    Jan 15, 2010
    Yes, 'under the chassis', means looking at the actual wiring connections to the bottom of the tube sockets. We're wondering if someone modified the wiring, to
    eliminate the 12AX7 tubes by replacing them with solid-state components (like transistors).
    A 'schematic' refers to a wiring representation of what's there in the form of a drawing.
    GonzoEngineer, no, not artillery.
    I'm sure you know, but for others who don't, a short round is an artillery shell that
    detonates prematurely after it's fired. Anywhere from when it leaves the barrel, to anywhere
    along the line of trajectory, before it hits the target. So it can be as dangerous to the
    gun crew that fired it, as it would be to a potential target downrange.
    I was a Marine. The nickname was given to me in an unflattering connotation.
    When they sent me out on a mission, I sometimes had a tendency to engage the enemy, when
    found, before I actually arrived at my assigned destination. Sometimes resulting in a
    delay in the accomplishment of the assigned mission.
    'Going-off', before reaching the assigned target, similar to an artillery 'short round'.
    I never lost the nickname, am still called that by the few of us still left, and just
    reminds me who I am.
     
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