I just joined and need help. I'm trying to fix the amplifier in my Chicago coin speedway arcade machine. It basically works but it has a bad hum in it. I did replace a couple capacitors that were in bad shape but the hum is still there. I finally checked the two germanium transistors in the preamp stage and they both seem to be shorted or out all together. I did order a couple new ones but my problem is I think the schematic is not correct. I'm going to replace the 2N2429 transistor and the A104 transistor. What's bothering me is the schematic calls for an A104 transistor which is a PNP transistor. The symbol shows a NPN transistor. Can someone tell me what is really suppose go in that spot?
you should recap all the capacitors considering its that old first. any leakage current at c1, c2, and c7 will really make it hum. I doubt that the transistors have go bad. Because you would have to physically remove them (or the resistor around them) to really test the transistors.