With TJ Byers
I have an old Minerva radio — at least that's what it says on the little plate just below what used to be a glass dial that runs across the top of the radio.
I would like to get this up and running, but have no schematic or even a model number to give you. It is a tube-type radio with six tubes and two rectangular cans mounted on the chassis. The front of the radio has three knobs: it appears that one is for on/off/volume and one is for tuning. The third, I don't know what it does. I'm able to get the filaments to light, but instead of music, I get a loud hum. I am sure that the capacitors are dried out and need to be replaced. Any help you can provide about this relic would be appreciated.
It sounds like your antique is a typical AC/DC, superhet radio from the post WWII era. You can identify this breed by looking at the tube numbers, which should include a 35W4 and a 50C5. And you are quite right about the hum: the electrolytics are bad. However, the rectangular cans you see on top of the chassis are not electrolytics, but instead IF transformers. If you turn the chassis over, you'll probably find a paper electrolytic riveted to the chassis via a metal band. It may be a two- or three-section device (it contains more than one capacitor), which can be replaced with single electrolytics. However, you need to replace all the sections, even if only one is bad, because they share some parts in common and there is a good likelihood that the other sections will fail soon. The values typically range from 30uF to 80uF at 150 volts. However, finding an exact replacement isn't necessary. Any capacitance of equal or slightly larger value will work. Same for the voltage — equal or higher. Be sure to observe polarity and dress the leads with shrink tubing. A good source of tube-type replacement capacitors is Just Radios at www.justradios.com/capkits.html. By the way, your mystery knob is a tone control.