If you just brought home an antique radio, you're probably dying to play it. That could be a mistake, however, unless the set was already playing when you bought it. If the radio has a short circuit or defective component, turning it on may further damage the set or even start a fire. You should always check an unknown radio for problems before you turn it on—otherwise, "firing it up" may be a sadly literal experience! The same goes for any radio that has been sitting around for years, since some components deteriorate over time. This page gives some tips on how to safely power up your antique set.

Preliminary inspection

First, check the power cord for cracking or fraying. Next, remove the cabinet back and look inside for obvious problems. (If you're shopping at a store or a busy swap meet, the owner may not be willing to let you pull the set apart. If so, at least try to peer in through the back. Even a little information is better than none.)

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

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, plan on repairing the set before you play it.

Removing the chassis

If your radio passes a cursory visual inspection, you should next remove its chassis from the cabinet for inspection. (The chassis is the metal box on which the electronic components are mounted.) Pulling the chassis is usually a matter of sliding off the knobs—and a dial pointer, in some cases—and removing a few screws from underneath.

Before you remove anything, however, get out some baggies and masking tape, so you can label every piece as you remove it. Don't trust your memory! If things look complicated, snap some Polaroid pictures, make a sketch, or take notes to guide you in reassembling your treasure. If at any time you hit a bad roadblock or feel like you're in over your head, don't be ashamed to reverse your steps and let a professional take over. It will be cheaper to repair an intact radio than to reconstruct a "basket case" of jumbled parts.

Many knobs slide off using gentle pressure. Check before pulling, however, in case there's a little setscrew securing the knob to its shaft. As you slide the chassis out of the cabinet, be careful not to break any wires leading to antenna, speaker, or other components on the cabinet. If you need to disconnect any wires, label both sides of the connection to guide you in reassembly.

If the radio chassis is dirty, take this opportunity to whisk away dust with a soft brush. You may be tempted to polish dirty glass tubes, but that doesn't matter. A little grime on the outside of a tube has no effect on its performance, and polishing may rub off its ID numbers, making it harder to identify a replacement if that's needed.

After you slide out the chassis, turn it on its side, or upside down, whichever is more secure. Brace it if necessary to avoid falling over. Some chassis have a metal plate covering the bottom, which you should also remove at this time. Work under a bright light so you can see everything clearly.

The chassis is out—what should I inspect?

Again, if you see anything that's obviously broken, disconnected, or burned up, you need to correct the problem before turning the set on. Here are some specific problems to look for.

• Power cord. Inspect the entire cord (not only the ends) for any evidence of failure. Rubber cords get brittle with age, whereas cloth-covered cords fray. Damaged power cords are easy to fix, and very dangerous to leave uncorrected.
• Paper capacitors. Paper-covered capacitors fail so frequently that experienced restorers often replace every one in sight, whether or not they look bad. These are usually small, paper-covered tubes with waxy-looking ends and wires coming out the end. Capacitors may deteriorate under humidity and other environmental factors over time, even if the radio hasn't been used. Or they may have failed as a result of normal operation. If the wax has melted and run out, that capacitor has already failed or is about to fail. Plan to replace it to avoid damaging other components. While you're at it, you might as well replace all its paper-covered brethren, too.
• Wiring. If you see any broken or disconnected wires under the chassis, go straight to the repair shop without passing Go (or applying power!).
• Tubes. Unless a tube is broken, you can't tell much about it by looking at it with the power off. A silvery or black color inside the glass is not evidence of malfunction. Unlike capacitors, tubes don't deteriorate from age, so you shouldn't assume that a tube must be replaced just because it is old. Despite popular lore, it is not necessary to replace all of a radio's tubes. I have restored dozens of radios, and very rarely have needed to replace tubes.
• Resistors. These are usually little hard cylinders, with colored rings painted around their middles. Some failed resistors will look burned or even have chunks missing, others may look normal. Resistors tend to be more reliable than old-style capacitors, so it is not common practice to replace them wholesale, even if one is obviously ruined.
• Transformers. Fairly large, squarish or rectangular metal components, with four or more wires (often color coded). If black waxy gunk has leaked out of a transformer, or if it looks obviously burned, you should at least test it before turning the set on.
• Tuner. Twist the tuning shaft and make sure the tuning capacitor moves freely throughout its range. (The tuning capacitor is a gadget with a series of flat metal plates that rotate together on a common shaft.) Many tuning mechanisms use strings and little pulleys. Make sure that the strings are not frayed or slipping.

Before turning on the power, experienced restorers will often clean the controls (volume control, tone control, tuning capacitor, etc.) using DeOxit or an equivalent spray cleaner. This is a routine maintenance step that you might as well get out of the way now. It can eliminate scratchiness in the volume control, gunk in the bandswitch that may make some bands weak or silent, or tuner gunk that may make the tuner hard to operate. But it's not absolutely essential solely for purposes of checking out the radio. Just keep in mind that some very common problems can be remedied by this simple cleaning.

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

If the radio passes visual inspection, it's time to switch it on. An experienced restorer will do this using a gadget called a variac (autotransformer) which lets you slowly increase the current over the period of a few hours, watching for any danger signs along the way.

If you don't have a variac, there are repair books out there that explain how to build a cheap homemade substitute.  If you don't have either one, you'll simply have to turn on the switch and cross your fingers. If the set is still out of its cabinet, be extremely careful to avoid shocks. Slip the knob back onto the shaft of the on/off switch. Don't touch any metal parts of the radio while the set is plugged into the wall, even if the radio is turned off.

Turn the volume about halfway up, and tune the dial to a strong local station. Within about fifteen seconds, the tubes should begin to glow with a faint orange color (unless they're metal-cased, of course). Watch closely for anything unusual. A slightly hot, dusty smell is normal, but a strong burning smell indicates trouble. The same goes if you see or hear any arcing (sparking) sounds, which may indicate a short circuit or failed component.

If the radio plays normally, take a moment to congratulate yourself. But you may not be out of the woods yet.

If you hear a noticeable background hum, that is caused by bad or limping filter capacitors in the power supply. In some cases, it's possible to "re-form" these capacitors electronically, bringing them back into acceptable operating condition. This requires either a variac or dim-bulb tester. The basic idea is to start playing the radio at very low voltage, then gradually increase the supply voltage over a period of time, giving the capacitors a chance to reform. If you have test equipment, you can monitor this process and determine exactly when to increase the voltage. As a practical matter, as long as you do it slowly, the process should work. I have done this with a number of radios, and it actually works in many cases.

To reform the filter capacitors, turn on the radio and plug it into your variac or dim-bulb tester. Start out at the lowest voltage (for example, 10 volts on a variac, or using a 15-watt bulb in the dim-bulb tester). Then, over a period of hours, gradually increase the voltage until you reach normal operating voltage. I have often done this over a 24-hour period. Whether you take that long depends on your patience, I guess. If you are using a dim-bulb tester, you gradually substitute bulbs of higher wattage (25 watts, 40 watts, 60 watts, etc.) to increase the voltage.

That's it! If you're lucky, the hum will be gone by the time you reach normal operating voltage. If not, you haven't lost anything except a fraction of a penny's worth of electricity.

Whether or not you use the reforming technique, once the radio reaches full power you should leave the power on and babysit the radio for at least fifteen minutes. Some times a component will not misbehave until it reaches full operating temperature, which will take a while. If you notice any change in performance, record the symptoms and watch for further changes. These may include fading in or out, changes in volume, buzzing or crackling sounds, or the loss of power.

After about half an hour, the set should have stabilized. If it works acceptably, enjoy! If not, it's time to crack open your repair book, hire a restorer, or just decide to enjoy the set in its non-working condition.