If the voltages are correct, ie. ~.6-.7 VBE, VC ~1.9, then chances are your transistor is working properly, so changing it will most likely not help. You say you aligned per the manual, can I assume you had the AM signal source suggested in the tuning guide (if not you will have a tough time getting back in tune) ? Have you tried an external AM antenna? If anything, I would suspect poor solder joints on the AM ant L6. If I recall, those old antennas had funky wire. My dad had one of those old GE radios in his garage to listen to the games, his also had the shortwave bands.