Well some more head scratching and some potentially bad news. First the bad news...
The original speaker in this radio was a 10" field coil speaker. Some PO replaced it with a 12" field coil speaker. I was excited to get a chance to play with a FC speaker but alas I made a couple of measurements today and it don't look good. The field coil measures about 5M ohms. Too high.
and the voice coil with one leg of the OPT disconnected measures 0.3 ohms. Rats, open field and shorted VC. Maybe what ever took the unit out of service took out the speaker as well.
This is a design with the basket used as a common and an insulated connector through the basket for the + VC connection so it is possible that the problem is in the pass through. I haven't disconnected from the pass through to check yet but I got a bad feeling about this one. The connections to the FC are covered by the insulating paper on the coil so I could not connect directly to the coil to check (could be bad connection). I tried to get a closer look by removing the U plate which is held on by four screws but when I tried to lift it the coil was coming with the plate and I wasn't ready to deal with disconnecting the VC and lifting the field coil off of the VC.
We shall see what happens there. I do have some PM speakers that I can substitute and a PS choke from an electronic organ so maybe I can convert without much expense. Still... would have been nice. The choke I have did not feed the plates on the organ but it did feed the screens of the 6L6s and 30+ each of 12AX7 and 12AU7 so I hope it has enough current capability. If the speaker is damaged of course the OPT may be toast as well. Again I may have a suitable (actually overkill) replacement available or can pick up something on the bay.
Now for the scratcher... As I was replacing caps in the output circuit I was using the Sams schematic to check my work. I was careful to remove only one item at a time and keep close track of where the leads went but I got to a point where things really didn't look right and I thought that I had mixed up the connections. Specifically in the tone control circuit. As the schematic shows there is to be a variable resistor in series with a cap across the output plates and a second cap bypassing that series string. The first confusion was that on my unit the VR/cap string is inverted with the resistor to V6 and the cap to V5. No big deal as it works the same either way but it was a bit hard to see that at first given the way the P-P wiring was done. The real kicker is that my unit has two .002uf caps. Instead one .002uf cap from plate to plate there is one cap from each plate to ground. What would be the reason for doing it that way? Is it equivalent?
Kind of a detective job now. If the speaker is fried we will want to know what happened. My first guess had been that a tone control cap had blown shorting the plates together but that should not have taken out the speaker.
mike