In addition to writing once in a while, I read a lot of blogs. They’re about a quarter political, a good bunch of news, about a quarter are photo feeds, and the rest are life interest and hobbies.
One of the more interesting ones is “Art of Manliness” which runs all manner of short and frequently humorous how-tos on topics like shaving with a straight razor, catching a horse, fixing things on your car, you get the picture. They recently put up a great article about re-purposing a broken antique radio into an external speaker for an MP3 player.
When I encounter a broken antique radio, my first instinct is to fix it up and add an input for the iPod but sometimes they’re just too far gone to save or aren’t valuable enough to spend a dozen or more hours repairing. In that case, tapping into the radio’s volume control and re-using its existing speaker is a good alternative and is usually a reversible modification. A lot of purists might complain about ruining an antique to make this repair, but it’s a reversible modification and let’s face it – fixing the radio up well enough to receive a signal and then using an AM transmitter isn’t going to sound nearly as good most of the time, anyway.
Around WW2, they changed how antique radio speakers work. Before then, speakers were electrodynamic using a field coil instead of a magnet. Since they have no magnetic field if they’re not fully powered by a very high voltage, they won’t play sound – you need a permanent magnet speaker. I mentioned this to the author and he updated the copy of the page to reflect this important information that might have resulted in a lot of disappointment for someone who used the wrong type without knowing:
Important Note: Commenter J.W. Koebel brought to our attention that if you want to use the radio’s original speaker like we do in this project , the speaker needs to be a permanent magnet speaker. Radios from about the mid-1940s and on should have permanent magnet speakers. Earlier radios used electrodynamic speakers. Our amp won’t work with electrodynamic speakers.
How do you know if your old-time radio has permanent magnet speakers? Check the back of the speaker. If it has 2 or 3 wires going to the speaker, it’s a permanent magnet speaker.
Better-known gadget blog Lifehacker picked up the story, and devoted about 1/4 of their summary article’s copy to that same warning.
Two caveats: Make sure your vintage radio is not terribly valuable before you take it apart and also make sure the speaker in the old radio is a permanent magnetic speaker and not an earlier electrodynamic speaker that won’t work with the new amp. If 2 or 3 wires are connected to the speaker, it’s a permanent magnetic speaker.
That’s pretty cool. I didn’t think much of it at the time, but I’m glad some of my advice will help fellow hobbyists have a successful project. (Also, this is my blog’s 100th post!)