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I'm almost done reassembling this BT-15 and have a question about Q8. Q8 looks correct per the attached schematic but the board I have appears to have the collector and base wires swapped?? The 2N3903 (Q8) is a TO-92 with an attached heatsink. With the leads facing you and the "flat" side of the HS down - pinout is B,C and E. The board I have has the collector lead attached to the center wiper of VR8 and the base is connected at the node of R48/45. All the connections look like they were made at the factory????
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2n3903 pin out is EBC, not ECBOriginally posted by Enzo
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Originally posted by g-one View Post
opps! Sorry Q8 is 2N3403 - pin out is BCE as oriented in my note.Comment
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OK, 2N3403 is listed as ECB pinout, but have you verified this with your meter? People do re-use the heatsinks and put other transistors inside there.Originally posted by Enzo
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Play it safe.
Rather than guessing:
1) re re re check bias transistor pinout, first with datasheet, then actually measuring it.
2) place it so emitter goes to Q10 base, collector to Q9 base, base to bias trimmer cursor.
No matter how you have to physically orient it or have to twist some lead to fit the proper hole.
This way you are forcing it to be oriented electrically the correct way, even if you use another type of transistor with different pinout.
3) always use a lamp bulb limiter on first turn on, doubly so because you've been messing with bias.
An error here can burn your output transistors in what? ... a millisecond?
No need to worry, just work slow and safe.
After you got reasonable bias and amp works, you can skip the bulb limiter and plug straight in the wall.Juan Manuel FaheyComment
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