Tech Square

Posted by Marty (A) on July 13, 2006 at 19:25:54

In Reply to: Dead output transistor wasn't dead at all . . . amp repair posted by JTB on July 8, 2006 at 17:10:29:

When troubleshooting power amps, I avoid going through a box of fuses and a box of new output xistors by inserting an incandescent lamp in series with the AC input. Depending on the amp's normal idle current drain, I choose a lamp wattage of between 60 to 100 watts. A short in the amp will light the lamp brightly but should safely limit the current through the outputs. Sometimes I use an old 150W photoflood if the device I'm working on draws significant idle current. When cold, a filament has pretty low resistance so I also use a 'Variac'.