Capacitors

I'm going to stray a bit from the usual computer-related post, and go more general. I bought an old dual-power radio at an estate sale the other day for 50¢. Its pretty beat up, and it had 4 batteries in it. Two were Duracell and two were Energizer. Based on the design style of them, I'd say they had been in there for about 20 years. I got the radio home, took out the batteries and tried it. It worked, but there was a noticeable buzz in the background, and there was a lot of static in the volume knob.

The static problem is extremely common in older radios, it is from dirt in the volume control, that is easily cleaned out with some contact cleaner from Radio Shack (WD-40 can be used, though it generally isn't recommended).

The buzz for the experienced person can be quite difficult to diagnose, and sometimes could just be written off as interference, but it was the same exact sound on AM and FM, at all frequencies. I took a quick look at the components on the circuit board and saw a bulging capacitor (red arrow in pic. 1). Its harder to tell with these older capacitors because there's no relief grooves in the metal, its completely sold. I bought a replacement 100μF electrolytic capacitor at Radio Shack about $1.30 (almost three times what I paid for the radio...). I de-soldered the bad one, popped in the new one and soldered it in. I had to re-solder the wires on the AFC switch because they fell off while I was handling the circuit board. After the repairs, I plugged it in and tested it, it sounded and worked as good as new! (I can't really fix the beat-up look, lol).

I think the approx. $1.80 investment was well-worth it, the radio comes in very clear, and has decent sound for the build quality. I am able to pick up WBCT 93.7 FM (B-93), which is about 90 miles away from where I live, in addition to that AM reception is exceptionally good considering all the interference in my house's electric. These 3o to 40 year old dual-power radios have some of the best AM reception of any Radios I have owned (note the rather large bar antenna). It is old enough to not have any IC's, but is new enough to use 5% tolerance resistors throughout most of the circuit (there's like one or two 10% tolerance resistors, but they are a bit higher wattage than the rest). It also has a compact tuning capacitor (the clear plastic thing in pic. 1) as opposed to the big old metal ones that were common through the 60's, and used in the 70's in larger radios. Also, it doesn't have a voltage source auto-select, there is an AC/DC switch on the left side.

I can't find much information about this radio. It was made in Hong Kong, but most components were made in Japan. The brand labeled on the front is "milovac." I've never heard of it before, but there was a search hit in Google Books for a 1972 Issue of Billboard magazine saying that Milovac 8-track players are made by Aiwa, and re-branded for the US and Canada markets. I have an Aiwa mini hi-fi system made in 1993 that is decent, but not outstanding. I'd say this radio is of pretty good build quality.