I recently recieved, for free, a broken 15 watt combo amp. The brand is Performance Plus, and the model number is gb12p. I would say the amp is over 5 years old. It hums, does not play, and smokes out of the input hole when turned on. The speaker, an 8 inch, works just fine when I hook it up to my other amp. Removing the head portion reveals that the smoke is coming from a 5 pin transistor that is attached to a heatsink. The chip has on it "MDA 2030". Following the path on the PCB leads me to a missing diode which I believe, based on the solder joints, is supposed to be there. What I need to know is: Where do I buy a new transistor? What type of diode, if any, should I use if I'm to replace the purloined one? Where can I buy said diode?