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The best transistor replacement

b139b

Hello everyone. Hope you all are doing well Thumbsup
I need some smart input from you... I am looking for some replacement transistors for my old tape recorder. The recorder sounds like a thunderstorm, so I think one transistor is bad. Since those transistors (BC330C, BC237B, BC238B) not are available anymore, I am looking for replacements.

In this case, since the design already is given, is "typical hfe" the parameter witch is most important to match with the original transistor? - To keep the same amplification steps. 


All maximum-voltages must of course to be the same or higher to the original.

I have some BC550C with hfe=420-800. Is it correct to think that the typical hfe for the BC550C is in the middle of this values =610 ? Too much amplification in my case?
Any input is appreciated Blush
Christian

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  • Thank you all for your replies! Great community! 

    The Thunderstorm is heat depended...came when I thought the player was fixed after the backlid was on. I have changed all electrolytes and C2. With a oscilloscope/RTA I can see that the signal is ok at the left side of C2 but the noise is present at the right. I have tried to find the faulty component by knocking on the components, potmeters too. Cool them with freezespray... heat with a heatingun but no component changed clearly.

    Thanks for the link to BC237B Blush

  • in reply to b139b

    Right side of C2 goes with the wire somewhere up high - could the noise come from there?

  • in reply to ggabe

    Goes to the Auto level part. I think they rectify the signals an use this to set the recording level automatically. image

    Could be, cause the other channel has made a "bump" (... oh, my English Rolling eyes) onces or twice. But very seldom. Could be something else too. 

  • in reply to b139b

    Is the issue happening with or without auto leveleing, or in both cases? T6/T8 seems serving the leveling/regular path. I would look at replacing C25/C26, perhaps before doing it just to put a known good cap in parallel to see if it reduces the noise. Are the voltages across R77 and R78 equal?

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  • in reply to b139b

    Is the issue happening with or without auto leveleing, or in both cases? T6/T8 seems serving the leveling/regular path. I would look at replacing C25/C26, perhaps before doing it just to put a known good cap in parallel to see if it reduces the noise. Are the voltages across R77 and R78 equal?

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