[David]

   
I do not know of another source for a better copy of the sch than the one from Nag. Air. The problem with Beitman is they did not do every model radio but there copies are clear at least my set. I have the complete set of Beitman and try and post info that I hope is useful. The resistor on the plus side of the sel rect is around 22 ohm on most of the sets from Z  that are AM/FM table models of this time period. The ones I have worked on will replace with a 50 ohm  at least 5 watts better to go with 10 watts. Thinking about what you said about the sound, try taking a second speaker let the set warm up and using jumpers connect to the output for a few minutes if the sound coming out of the 2nd speaker is clear you may have dirt and dust around the voice coil. Try replacing the cap without the shield it will probably work. Going to add another from Beitman has the 4 sec filter cap hope you find it helpful. David