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  • Geloso G213A

    Hey Guys,
    I I saw a Geloso G213a for sale locally for a low price.
    Is this a good project to convert it into a guitaramp?
    Thx!


  • #2
    Looks good for a conversion. It has fixed bias for the outut stage and DC heater supply for the preamp.
    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
    REMEMBER: Everybody knows that smokin' ain't allowed in school !

    Comment


    • #3
      thx, that's what I was thinking....
      Is a conversion to a 5E3 circuit realistic?
      .

      Comment


      • #4
        The problem with the 5E3 is the 9 pin preamp tubes. You would have to fabricate a cover for the Octal socket holes to install the 9 pin sockets. Weber sells such an adapter, but they are frequently out of stock. I would stick with the Octal preamp tubes. There are earlier versions of the 5E3 that used octal preamp tubes. I think the 5C3 is one. Lots of possibilities with two dual triodes and a pair of 6V6s.

        There is no currently make 12SL7, but you can get the 6SL7 which is just a 6V version of the same tube. You should be able to find New Old Stock on the 12SL7 and they should be fairly inexpensive because demand is low.
        WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
        REMEMBER: Everybody knows that smokin' ain't allowed in school !

        Comment


        • #5
          5c3 might be interesting, but I see 2 problems:
          1 As I search the web there seems to be a general consensus that a 5c3 circuit doesn't work that well with pedals.
          2 How do I organise the heater supply. In the original schematic of the donor amp the heaters of the preamp tubes are in series (Total 24V) Can I reuse this part of the circuit with two 6SL7's?
          The common noval tubes (12AX7, 12AY7) have center tap on their heater, so they can run on 12V

          Conversion plates octal 2 noval aren't a problem. A local store has them.

          thx for your reply!

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          • #6
            I finally bought the Geloso last week
            Also got some ancient DIY amp, but it has good glass and transfos. (2x 6SL7 2x6V6, all RCA)

            Click image for larger version

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            • #7
              Two weeks ago, I finally did the conversion. I'm very pleased with the result, it sounds very nasty.

              The inputs are lo & hi sensitivity. The switch below the inputs selects the channels: instrument, mic & linked.
              On the back, I added a 230V IEC Power inlet. I also removed the output terminal strip and replaced it with an ordinary output jack and a 4-8-16ohm switch.

              I used the stock 5e3 schematic, so I replaced the octal preamp sockets with noval ones.

              Th only problem I currently have, is the instability of the DC preamp heater supply. I temporarily need to use a 24V voltage regulator until I redesign this part of the heater supply .


              Click image for larger version

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              Last edited by Sk10; 09-09-2012, 09:44 AM.

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