No announcement yet.

Determining the type of old Gibson transistors 1970's

  • Filter
  • Time
  • Show
Clear All
new posts

  • Determining the type of old Gibson transistors 1970's

    Greetings,......I am repairing the circuit board on a 1970's Gibson electric guitar. I've determined that one of the transistors is bad. I have tried to cross-reference the part on Mouser and Digikey's websites....with no luck. Does anyone have a good way of determining what this part is and finding an adequate replacement. The markings on the device are SF 51234 then 802 underneath.....the circuit board indicates the position for D S and G. There are a number of these on the board. I tested a couple of the others in my multimeter....they seem to measure out with a gain of 970 on the PNP setting. ....hopefully I've done this correctly! Any help would be greatly appreciated.


  • #2
    What exactly is the board out of?


    • #3
      The numbers are house numbers and won't show up in catalogs.

      The DSG - drain, source, gate - on the board indicates it is a JFET. You'd have to determine N or P channel from voltage polarity. If your tester covers JFETs test them that way.

      Most any general purpose JFET ought to work, I'd think, assuming correct polarity.
      Education is what you're left with after you have forgotten what you have learned.


      • #4
        ....the guitar is a Gibson RD.

        I will test the polarity and see if it is N or P channel....PNP on the multimeter isn't = P channel FET?

        Thanks for the replies.


        • #5
          If you don't know whether the pcb drain is positive or negative, how do you know the transistor is bad?
          If it is a gain stage you would probably need to bias it anyway, so you could probably get a J201 to work. Hard to know what the gain/transconductance of the original transistor was, regardless of markings.


          • #6
            The RD Artist Schematic shows them as N-Channel jfets. It also states that they are "selected" components.

            How have you "determined that one is bad"?

            What model RD guitar, and what's the problem?


            • #7
              ....I had originally determined/found the bad part by testing the voltages with a multimeter....the bad one seemed "off" in relation to the others.

              I tried the J201 in its place. It now works beautifully!

              Thanks for your help.