I am going to acquire a 550-ohm, 50MADC new old stock choke. Is this value close enough, or should a 50-ohm resistor be added in series?
While we're on the subject, does anybody know the proper impedance of the voice coil for this radio? I tested it using a 600-ohm resistor and a speaker with a 4-ohm voice coil (it worked), but I have an 8-ohm speaker that I would rather use.
The output transformer, luckily, is attached to the chassis and not the speaker.
Thanks in advance for any help, which is most sincerely appreciated.
That choke should be ok. Close enough. You can see what B+ voltages the schematic shows and see how close you are after putting in the choke. Remember that AC mains are higher then when your radio was made. Typically 125vac now as opposed to 110v.
The 8 ohm speaker will probably work, But it most likely was a 4 ohm original.... so there will be some mismatch.
The square of the turns ratio of the output transformer times the speaker impedance will create a reflected load to the output tubes.
Those 6k6 tubes typically require an 8000 ohm load.
So if you have an output transformer with a 45:1 turns ratio.. and then if you square 45 it equals 2025 times a 4-ohm speaker = 8100 ohms.
So...if you change the speaker to 8 ohms the reflected load will double to 16,200 ohms
The best explanation of this is here at this site. It's an easy read and worth it:
http://www.radioremembered.org/outimp.htm