I picked up a cool-looking old tube radio the other day. Unfortunately it doesn’t work. When you turn it on, instead of a signal, you hear loud buzzing. Here’s what causes tube radio buzz and how to get it fixed.
Of course we assume any problem with a tube radio is the vacuum tubes. But loud buzzing is usually caused by bad capacitors, not tubes.
Tube radio hum vs buzz
When you hear radio hobbyists talk, they talk about humming, not buzzing. They refer to hum as pretty much anything that isn’t the sound of a radio broadcast. When I think of a hum, I think of the sound a refrigerator makes. The sound this radio makes sounds more like the sound of my neighbor cutting up lumber for his deck.
When you hear this, turn the radio off and unplug it. The problem won’t get better on its own. What you’re hearing is the sound of dirty electricity, and that could eventually damage other components inside the radio.
If you’ve already replaced the tubes and the buzz still didn’t go away, replacing the tubes didn’t hurt anything. We always assume tubes go bad because we grew up hearing how unreliable tubes are. I sure did.
Re-capping tube radios to fix tube radio loud buzzing
To fix the loud buzzing, the capacitors inside the radio need to be replaced. The shelf life on capacitors is usually around 20 years, and most tube radios have that number doubled or tripled by now. And while tubes won’t go bad just sitting around unused, capacitors will.
Capacitors go bad in more than just old radios. If you’ve ever had a flat-panel TV go bad on you, there’s a pretty good chance that was worn-out capacitors too.
Capacitors aren’t expensive. Typically they cost a dollar or two, and a tube radio probably has five or six of them inside. But replacing them does require soldering, and frequently some re-wiring, because frequently the modern capacitors available today aren’t the same size and shape as the old ones. Sometimes radios had combination capacitors inside, with several capacitors inside one unit. We don’t do that anymore. To replace one of those, you have to wire up a replacement using several appropriate modern capacitors.
If you’ve replaced capacitors on other electronics projects before, this isn’t much harder. You should be able to find a schematic at Nostalgia Air, use that to find appropriate values for your capacitors, and replace them. If you’ve never done this before, you’re probably better off finding an electronics technician, or perhaps a small appliance repair shop. The labor will cost more than the parts. But a tube radio with sentimental value is worth fixing.
With new capacitors in place, you can expect the radio to last 25 years before needing service again, maybe more.
And then, if the case is made of Bakelite like many old radio cases were, and you want to make it look good, here’s how to clean and polish Bakelite.