09-02-2015, 12:15 PM
Eric, you can try the transformer you have, but I don't think it will work connecting the low impedance secondary to the 2500 ohm speaker.
What might work better is if you use that transformer, but do not connect anything to the secondary speaker winding. Connect the primary as usual to the plate of the 71A and B+. Then connect a .47 uF film cap from the plate to one speaker terminal, the other speaker terminal to ground. The cap will block DC but allow the high impedance audio signal to pass to the speaker. This would effectively be the same as the choke coupled speaker output used in the other radios i mentioned.
The output transformer has a high inductance, and if the secondary is left disconnected it makes a very good audio choke.
What might work better is if you use that transformer, but do not connect anything to the secondary speaker winding. Connect the primary as usual to the plate of the 71A and B+. Then connect a .47 uF film cap from the plate to one speaker terminal, the other speaker terminal to ground. The cap will block DC but allow the high impedance audio signal to pass to the speaker. This would effectively be the same as the choke coupled speaker output used in the other radios i mentioned.
The output transformer has a high inductance, and if the secondary is left disconnected it makes a very good audio choke.
