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Mystery transistor

topic posted Sun, July 2, 2006 - 2:30 PM by  Unsubscribed
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I'm impressed by the number of electronics wizards in this forum. Maybe you can help me identify a source or equivalent for this transistor.

It is a T0-3 type power transistor, manufactured by RCA.

The numbers read: 7 0100 7628

It is one of eight output transistors in a "Kustom Stereo-X" PA system.

Back when I used to work on amps regularly (about 25 years ago!) I could run down to the electronics parts store and get these over the counter. Whic is something I had to do regularly with Kustom amps, as they liked to blow their power transistors. But I don't think RCA makes them anymore and I can't find anything on the web. Kustom amps has long changed hands and I don't think they have info on their old stuff anymore.

They appear to be NPN transistors, but I don't have the schematic. This is the only one that is shorted. The amp blows a fuse the moment you turn it on.

This is a very solid looking 250 watt PA. I hope to make it work again.
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  • Re: Mystery transistor

    Sun, July 2, 2006 - 3:59 PM
    Hmmm...I wouldn't rate myself as much of an electronics wiz or much of a web geek either (others who know me might disagree, but hey it's all relative). Anyhoo, a couple of Google searches and a little bit of intuitive reasoning yields the following:

    www.vintagekustom.com/frame.html (source for vintage Kustom schematics)

    www.goldmine-elec-products.com/pr...asp (source for power transitors once you find a part number

    Dunno if this is what you were looking for, but it was a momentarily interesting research project for me.

    • Unsu...
       

      Re: Mystery transistor

      Sun, July 2, 2006 - 5:29 PM
      Thanks.

      Unfortunately, none of the amps they list are the same model.

      I suspect Kustom used the same power transistor in all their amps.

      But I have my doubts that the schematics identify it any differently than what is on the case.
  • Re: Mystery transistor

    Sun, July 2, 2006 - 4:14 PM
    Oh and there appears to be another vintage Kustom fan site that claims to have a schematic for your amp:

    www.broadwaymusicco.com/Kustom10.htm
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      offline 12

      Re: Mystery transistor

      Wed, July 5, 2006 - 8:22 PM
      My best guess is 2N3055. I've repaired a few guitar amps in the past and they all used the 2N3055 finals. Sometimes several. The 2N are dirty cheap and it may be worth to try if it works.
      There is usually a high wattage/low ohm resistor that dies with the finals, you should probably replace that as well.
      • Unsu...
         

        Re: Mystery transistor

        Wed, July 5, 2006 - 11:10 PM
        Thanks. I'll bet you are right.

        I fixed a lot of these old Kustom amps back in my day as a tech at the guitar store, and that transistor number seem right. It's just been so long, I could not quite remember anymore.

        Used to be, you could just grab a transistor book that had all the equivalents. Now you have to outbid someone on ebay to get your hands on one of those books. ugh.
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          offline 12

          Re: Mystery transistor

          Wed, July 5, 2006 - 11:29 PM
          > I'll bet you are right.

          I wouldn't be sure about that :-)

          Anyway, the 2N3055 was introduced by RCA. I've tried to download this paper:
          ieeexplore.ieee.org/search/wrapper.jsp
          but access to this journal is not included with my subscription.

          If you want to do an extra test, for peace of mind, you can try to cut the metal top with a dremel and expose the die. Do the same with a 2N3055 of the same vintage and they should look the same. Problem is that if they don't, you still have no answer since the two could be two different generations.


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            offline 12

            Re: Mystery transistor

            Wed, July 5, 2006 - 11:46 PM
            The exposed die should look like this:
            tesladownunder.iinet.net.au/LEDT...r.jpg

            Transistors manufactured in a different period might look different; this picture is claimed to be of a 2N3055 as well:
            www.fieldlines.com/story/20...5028/6819

            From what I remember (I've opened a few in the past, dead 2N3055 = poor man's solar cell :-) ) the die should look like the first one.
            • Unsu...
               

              Re: Mystery transistor

              Thu, July 6, 2006 - 12:32 AM
              I think I'll just pop one in and see what happens.

              Remember, this amp blows a fuse the moment you throw the switch. There could be a lot wrong with it, but a shorted power transistor like I have on this amp is the mostly culrpit on a Kustom.

              If I can't fix it, I've still got $50 to $100 worth of good project parts to salvage from it. Paid $15 at a garage sale. You ougtha see the transformer on this thing. There is some serious iron.
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                offline 12

                Re: Mystery transistor

                Thu, July 6, 2006 - 11:59 AM
                Good luck and keep us posted.
                At worst, it sounds like a perfect candidate for an Ebay auction :-)
                • Unsu...
                   

                  Re: Mystery transistor

                  Thu, July 6, 2006 - 4:13 PM
                  Ebay, no way.

                  I'm keeping it. The cabinet would make a great housing for a guitar ube amp I am meaning to build, and the parts will come in handy for that and other projects.

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