When Can I Turn On My Old Radio?

If you just brought home an antique radio, you're probably dying to play it immediately. That could be an expensive mistake unless the set was professionally repaired before you bought it.

If the radio has a short circuit or defective component, turning it on could further damage the set or even start a fire. You should always check an unknown radio for gross problems before you turn it on—otherwise, "firing it up" might be a sadly literal experience!

Even if the radio has been sitting unused for years, some components, notably capacitors, will deteriorate with age. Even a radio that looks "factory fresh" may still be unsafe or unreliable to play.

This page gives some tips on how to check out your radio before turning it on.

Spotting Gross Defects

A few problems can be spotted visually. For example, if the power cord is broken, cracked, or frayed, you must replace it before trying to plug in the radio.

Some other problems can be spotted by looking at the chassis. (This is the metal box inside the cabinet, upon which other components are mounted.)

Some radios have backs and others don't. If the radio has a back, you'll need to remove it to inspect the components (tubes, etc.) on top of the chassis.

The cabinet back is usually attached with a handful of small screws or clips. As you remove it, be careful not to break any antenna wires that may be attached. Some newer radios will have an integrated connector for the power cord, which unplugs the cord from the chassis as you (gently!) remove the back.

After the back has been removed, what should you look for? Gross problems include missing or broken tubes, and anything else that's obviously absent, broken, disconnected, fried, or massively corroded. If you see any of these signs, count on repairing the set before you power it up.

I won't explain how to remove the chassis at this stage, because, honestly, if you're a beginner you won't learn anything useful by looking under the chassis. And plugging in the radio outside the cabinet will only increase your risk of getting an electrical shock.

In almost all cases, the radio's electronic components—tubes, capacitors, resistors, etc.—will look exactly the same whether they have failed completely or they are working perfectly. When a radio is turned off, a dead tube looks just like a good one. A shorted capacitor looks just like a good one, and so on.

My radio looks fine. Can I turn it on now?

Let's say that your radio passes the gross visual inspection. Can you turn it on yet?

Many experienced restorers would not bother trying out the radio at this stage. Instead, they would remove the chassis and routinely replace most or all of the old capacitors. You can read all about this process in the article Replacing Capacitors in Old Radios. Whether you want to take this cautious approach is up to you.

At this stage, let's assume that either you have finished the capacitor replacement or you're willing to risk firing up the radio as-is. Either way, many restorers will power up the radio using a gadget called a variac which lets you slowly increase the voltage, watching for any danger signs along the way. If your variac has a built-in ammeter, that will let you monitor the amount of current drawn by the radio and quickly turn it off before that approaches a hazardous level.

If you don't have a variac, you can use an inexpensive homemade Dim-Bulb Tester. In addition to increasing the voltage by increments, a dim-bulb tester can also warn you of short circuits in the radio's power supply and prevent those from damaging the radio.

If you don't have either one, you can simply turn on the power switch and cross your fingers, but I advise against that practice, for all the reasons given above.

Once the voltage has been increased to full power, turn the volume control up about one-third of the way and tune the radio dial to a strong local station. Within about fifteen seconds, the tubes should begin to glow with a faint orange color. (Exceptions are metal-cased tubes, which have an opaque covering, or very-low voltage tubes such as those in old Zenith TransOceanics.)

Watch closely for anything unusual as the radio warms up. A slightly hot smell is normal, especially if the radio is dusty, but a strong burning smell indicates trouble. The same goes for any sparking sounds or smoke, which usually indicates a serious problem.

If the radio plays normally, take a moment to congratulate yourself, then turn it off until you have time to replace the capacitors (see the link above).

If you hear a loud humming sound that does not change when you turn the volume control, that is caused by failed filter capacitors in the power supply. The radio will not work until you replace them.

If the radio sounds OK, can't I just play it?

Sure, you can play an unrestored radio all you want . . . if you don't mind the risk that it will fail at any time without warning.

In my experience, most unrestored radios will conk out—typically with one or more failed capacitors—before long. And if you go in to replace that failed capacitor, it's only a short time before the next one will fail, and so on.

To get a radio that is safe and reliable to use every day, it's best to replace all of the old capacitors at once. If you choose not to do that, I strongly advise that you never leave the room while the radio is playing, or leave it playing overnight. It's just not worth the risk. A few unrestored radios might play for a long time without problems. Others can start on fire—it has happened to me!

©1995-2018 Philip I. Nelson, all rights reserved