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Topics - Felixl

#1
Hey, just bought a Troubadour amp for a few dollars. Owner told me it started to make smoke when he lit it.
I tested it. Both output transistors TIP41 and TIP42 were toasted. The TIP showed obvious burn marks. I replaced them and the amp seemed to work. But...
I later noticed that two .5 ohms resistors had been removed. Oddly, those where the resistors (see R223 and R223on schematic) connecting both TIP's emitters. So without those resistors both emitters were connected to nothing. But still, I got sound from the amp. It seemed to work, only maybe the input too sensitive and a tendency to distort if the guitar volume was too high. I wasn't sure if this is because the amp was designed only for mikes and acoustic guitar pickups.

Question 1 : Is it normal that the amp still makes sound if the emitters are not connected to anything?

Realising the 2 resistors were missing and guessing this might be why the TIP were toasted, I put back the two missing .5 ohms resistor exactly where there are on the schematic, no mistake possible, you can't miss the spots on the PCB.

And then : smoke!!! One of the resistors burned out and the TIP42 was fried.

I re-replace the TIP42 and took out the resistors and it seems to work. Or does it??

Does anyone knows what can be the cause of this? Thanks


SCHEMATIC :  [/img]