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Question on Gibson GA-16T and GA-18T amps

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  • Question on Gibson GA-16T and GA-18T amps

    I have bought an old (1960?) Gibson amp that I am trying to identify correctly.
    It has a 10" speaker, three input jacks, no output jack, tremolo, vol/tone/depth/freq control pots, and the following tube complement: 5Y3, 2 x 12AX7, 2 x 6V6. Serial no. is 110429.
    It bears the name "Explorer" and a tiny "Model GA-18" on the control plate.

    Now a few questions arise about the true identity of this amp.

    1) It has tremolo, so it should be a GA-18T and not a GA-18.

    2) In several websites I have seen descriptions/reviews of GA-18T amps with the same tube complement as mine. All except one (, where the original schematic of model GA-18T is different from my amp: it has a "monitor" output jack and totally different tubes, plus several others differences!

    3) The circuit of my amp is the same as model GA-16T available in .

    What is going on?
    Is mine a transition model?
    The best website on vintage Gibson amps that I am aware of ( is not useful to solve this mistery.
    Can anybody shed some light on this issue?
    Carlo Pipitone

  • #2
    Welcome to the world of Gibson amps. Finding two alike is a miracle. If the schematic matches the amp I have in front of me it is a glorious surprise. They often and without notice changed the innards of their amps. Not only could one Gibson model be really another under the skin, but sometimes it was really an Epiphone model, or the Epi was really a Gibson.

    I have the Gibson Master guide, and I cannot tell you how many times I have leafed through it looking for the tube lineup that matches an amp that doesn't match the schematic it should.

    Look on Schematic Heaven for the guide. It is under "schematic manuals" and is 177MB. That is a long download, but it covers a lot.

    And sometimes NONE of the drawings match There will always be similarities with parts of it, but sometimes it is some of one and some of another. My book has quite a few loose pages I have added where I drew out the circuit of a particular amp of some models.

    I don't think of them so much as transitions - though that might be part of it.

    I think they just looked at an amp as: two channel, EQs, trem and reverb. WHat the actual circuit was behind it didn't matter a lot to them.

    You got a drawing that matches, that is all you need. There is no story to find. it si a common dilema
    Education is what you're left with after you have forgotten what you have learned.


    • #3
      Thank you Enzo.
      I'll check that link inside schematicheaven.
      Carlo Pipitone


      • #4
        My "tweed" Explorer (a '60, I think), is marked as GA-18 but also has tremolo, and is a wonderful little amp. I don't remember if the schem is marked as 18 or 18T, but it does match the circuit.


        • #5
          I forgot to say that the schem I got was received from Gibson a few years back.....not from my later-received copy of the MSM. It does have the correct tubes for my unit (12AX7s and 6V6s).


          • #6
            I have schematics that came with amps - and didn't match them. I just tuck them into the master guide along with the rest of the loose stuff.
            Education is what you're left with after you have forgotten what you have learned.