Harmon Kardon SR900 transistors

[Mayday]

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

[silverD]

After a bit of googling, these appear to be H43020418. Good luck on your quest.

[fpitas]

Wow. Germanium PNPs, I guess? Maybe Ebay will have replacements.

[fpitas]

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

[Mayday]

yea I guess they are germanium. I just came across this.

https://www.radiomuseum.org/tubes/tube_h43020418.html

[Psycoacoustics]

https://www.ebay.com/itm/HARMAN-KARDON-CITATION-17S-PREAMP-REBUILD-AND-RESTORATION-SERVICE/332224314490?hash=item4d5a1cbc7a:g:iBIAAOSwDN1UMrm7

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

Good luck, Mark

[fpitas]

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.

[Mayday]

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

[fpitas]

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.

[Mayday]

What about a different geranium one.

[fpitas]

What about a different geranium one.

Sure. That's why I suggested you call that company I linked above. They may have a replacement.