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Harmon Kardon SR900 transistors

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  • Harmon Kardon SR900 transistors

    I recently acquired the amp stated in the subject. But it is missing on of the power amp transistors. I am unable to find a replacement for it so I have no choice but to replace all 4. All I know about them is that they are pnp. The part #'s dont come up with anything. Anyone have an idea of what I could use as a replacement?

    Thanks in advance

  • #2
    After a bit of googling, these appear to be H43020418. Good luck on your quest.
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    • #3
      Wow. Germanium PNPs, I guess? Maybe Ebay will have replacements.
      Francis

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      • #4
        Maybe these guys can help you: http://www.njsemi.com/products/gp-bjt?page=3
        Francis

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        • #5
          yea I guess they are germanium. I just came across this.
          https://www.radiomuseum.org/tubes/tube_h43020418.html

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          • #6
            https://www.ebay.com/itm/HARMAN-KARD...IAAOSwDN1UMrm7

            Contact my buddy Pat. He helped me with my Citation 16 17 and 18. He may be able to help.

            Good luck, Mark

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            • #7
              In a pinch you could redesign for silicon PNP transistors, but you'll have to redesign the bias circuitry to get a reasonable quiescent current.
              Francis

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              • #8
                Could I not replace them all with different ones? Like the one they sell on here? What would it do if I did.

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                • #9
                  Originally posted by Mayday View Post
                  Could I not replace them all with different ones? Like the one they sell on here? What would it do if I did.
                  Silicon transistors have a higher threshold voltage than germanium, so the quiescent bias would be off badly. You would have tons of crossover distortion.
                  Francis

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                  • #10
                    What about a different geranium one.

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                    • #11
                      Originally posted by Mayday View Post
                      What about a different geranium one.
                      Sure. That's why I suggested you call that company I linked above. They may have a replacement.
                      Francis

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