You can use an inductor, 5 or 10 henry choke, in place of the field coil. Most inductors will have lower resistance. It would be best to add a resistor in series with the indictor to make up the difference. The resistor should be 10 watts or more. It will get very warm.
A resistor alone can be used. In this case higher value filter caps may be needed to reduce hum.
When using a PM speaker connect two leads directly to seconday of your output transformer. The other copper winding you noticed is probably a hum bucking coil, used with field coil speakers. This coil cancels hum caused by ripple current going through the field.
Norm
:Hi all,
:I posted earlier about the audio output transformer being shorted. Actually, it's the field coil. This and a 40-130 are the first old radios I've attempted to work on, so I didn't really know the difference. (Common sense should have told me the field coil was the one centered on the speaker). I've seen other posts on the site about using an inductor in place of the field coil. The schematic says the resistance is 660 ohms. Can I use an inductor of this rating and what power dissipation should it have? Also, the audio transformer had one output going to coil of thin copper about 1/8 of an inch wide wrapped around the center of the speaker under the field coil. the other end of this coil connects to the voice coil on the paper cone. If I use a modern permanent magnet speaker, would I hook it up in place of just the voice coil and leave the thin copper strip coil hooked up in series? Any help would be appreciated.
:(Norm, if you read this, I haven't had a chance to check the oscillator coil in the 40-130.)
:Thanks,
:Bobby