[Today’s run: 3 miles]
We finished most of the re-capping of the old Silvertone console radio this evening. There are a couple of capacitors inside an IF transformer and I’m not sure what we are going to do about that.
Getting down almost to where we can fire it up.
The next thing to check was the speaker. This is an old field-coil type speaker, about 10 inches in diameter. Wouldn’t you know it, the field coil has no continuity.
You can look this up on wikipedia for the real information, but, a field coil speaker is different from a modern permanent magnet speaker. Modern speakers have a small coil of wire and which works with a permanent magnet to move the center of the speaker in and out. That moves the air and you get sound.
A field-coil speaker doesn’t have a magnet. Instead they use a coil of very fine wire as an electromagnet. The coil of wire does double duty as an inductor/filter to smooth out the power supply. So, the field coil acts as part of the power supply and as a speaker. Pretty slick idea. The problem is that if there is any trouble with the power supply, the fine wires in the field coil are the first to burn out. So you lose your speaker. And that is probably what has happened to ours. I took apart the field coil a little bit and could not find any obviously burnt place. But I may have to unwind half a mile of wire to figure that out, and I don’t think I have the necessary skills to wind it back up again even if I find the problem!
It is not impossible to convert to a modern speaker. You have to get a separate inductor to do the power supply filtering job. And then you get a permanent magnet speaker and hook everything up correctly and you are back in business. I think that is probably what we will have to do.