How to Replace Capacitors in an Antique Radio

by Jeff Grundy Google
    Vacuum tubes last much longer in antique radios than paper or electrolytic capacitors.

    Vacuum tubes last much longer in antique radios than paper or electrolytic capacitors.

    Jupiterimages/liquidlibrary/Getty Images

    Antique radios add a nostalgic charm to a room and may be worth a considerable amount of money if in working condition. As with many other products from the early and mid-20th century, manufacturers made radios from the era to last and provide years of reliable service. Consequently, working antique radios still exist and play broadcasts now as well as they ever did. If you have an antique radio that no longer plays, chances are good that replacing a few defective capacitors or tubes can restore the radio so that functions normally. Replacing capacitors or vacuum tubes in an old radio is not difficult, but it does require a bit of caution and attention to detail.

    Replacing Paper, Wax and Electrolytic Capacitors

    Step 1

    Unplug the antique radio's power cord from the electrical socket if you have not already done so. Leave the radio unplugged for at least an hour before continuing and opening the cabinet.

    Step 2

    Use a screwdriver to remove any retaining screws that secure the rear access panel to the cabinet. Remove the panel and pull the circuit board chassis for the radio out of the cabinet. Some chassis boards may slide in and out of the cabinet, while with some others you may have to remove retaining screws first.

    Step 3

    Inspect all of the capacitors in the antique radio and identify the faulty ones you want to replace. Many times, you can identify faulty paper or wax capacitors if they have leaks that cause them to appear gooey or melted. Larger electrolytic capacitors that are faulty often bulge or even blow out the top.

    Step 4

    Strip about one inch of sheathing from both ends of the insulated copper wire length. Wrap one of the stripped ends of the wire around the upper part of the screwdriver shaft and secure with some electrical tape. Secure the other end of the wire to a metal object with the tape to create a ground. The screwdriver must have a rubber or insulated handle.

    Step 5

    Touch the two leads of a capacitor you want to replace with the tip of the flathead screwdriver. If the capacitor still has a charge, you may see a small spark or flash when you touch the two leads with the tip of the screwdriver.

    Step 6

    Connect the alligator clips from the multimeter cables to the leads on the capacitor. Power on the multimeter and set its mode setting to volts. Ensure that the multimeter reads "0.00." If the meter shows that the capacitor is storing residual voltage, use the flathead screwdriver to discharge the capacitor again. Continue to discharge and test the capacitor until the voltage reading on the multimeter reads "0.00."

    Step 7

    Clip both leads on the capacitor as close as possible to the terminals in the circuit board. Remove the old capacitor from the antique radio.

    Step 8

    Purchase replacement capacitors for the antique radio. When purchasing new capacitors, buy modern polyester film, polypropylene film or metalized film capacitors with like microfarad and voltage ratings. You can replace all types of capacitors in an antique radio with any of the modern capacitor types.

    Step 9

    Plug in the soldering iron and let it heat up. Use the soldering iron to melt any old solder in the holes where the leads for the old capacitor went through the terminals in the circuit board.

    Step 10

    Use the needle-nosed pliers to wrap the leads on the new capacitor around the terminals in the circuit board. Crimp the leads to the terminals with the needle-nosed pliers so that they are secure and to ensure a metal-to-metal connection.

    Step 11

    Heat the terminals with the soldering iron and apply new solder to them.

    Step 12

    Replace other capacitors in the antique radio as needed.

    Replacing Vacuum Tubes

    Step 1

    Turn off the antique radio and unplug the power cord if you have not already done so. Let the radio sit and cool for at least four hours before continuing. Open the radio cabinet and remove the chassis board.

    Step 2

    Remove the tube's protective metal cap if it has one. You can remove the cap by twisting it counterclockwise and removing it just as you would a light bulb.

    Step 3

    Grasp the glass tube firmly with one hand. Lift straight up on the tube while gently rocking it side to side slightly. For tight-fitting tubes, this makes it easier to remove the tube from its receptacle. However, do not rock the tube more than 1/8-inch in either direction to avoid damaging the socket receptacle. Continue lifting up on the tube and rocking it gently until it breaks free from the receptacle socket.

    Step 4

    Purchase a new tube to replace the defective one. Your local electronics store probably won't have any vacuum tubes, so you'll likely need to buy one online. Note the markings on the defective tube and then visit websites such as TheTubeStore.com, Antique Electronic Supply and Triode USA. On the sites, you can usually find information about which types of replacement tubes are compatible with the defective one you removed from your antique radio.

    Step 5

    Align the pins on the bottom of the new tube with those in the receptacle socket. Push straight down on the tube firmly but gently until securely seated in the socket.

    Step 6

    Replace the metal cover for the tube if it has one. Replace other vacuum tubes in the radio as needed.

    Tips

    • You can purchase any capacitors you need to restore the antique radio from your local electronics store.
    • You may also be able to find compatible tubes in old televisions. Even if an old TV is not working, the power-rectifier tube or audio tubes are probably still good. In some cases, you may be able to find old nonworking TVs at thrift shops or garage sales for only a few dollars or get one free if someone wants to throw it away.
    • Vacuum tubes for antique radios can be hard to find and are often expensive. Therefore, do not replace one unless you are sure it is defective. Before considering replacing a vacuum tube in an antique radio, replace all the capacitors first. Vacuum tubes generally last many years unless damaged physically. In many cases, a vacuum tube that fails to light or heat up is the result of a bad capacitor in the same circuit.
    • Can-type electrolytic capacitors have negative and positive leads. Before aligning the terminals on the capacitor with the terminals in the circuit board, ensure that the polarity matches. The terminals in antique radios may or may not have polarity labels. Therefore, write down the orientation of the leads on the old capacitor before removing it so that you can match it with the polarity labels on the new capacitor.
    • It is not always possible to identify faulty capacitors just from their appearance. However, many antique radios contain 10 or fewer capacitors. Consequently, many antique radio enthusiasts and restoration experts recommend replacing all the capacitors when restoring a unit.

    Warnings

    • If the antique radio has been sitting unused for a number of years, the capacitors probably won't have any charge remnants. Nevertheless, it is always best to discharge a capacitor before attempting to handle it or clip the leads to the circuit board. This is especially true of capacitors used in the power supply circuit or ones connected to the power rectifier tube. These types of capacitors store much higher voltage charges than do paper or wax capacitors and may retain them for many years in some cases if not properly discharged. Failing to discharge a large-capacity capacitor before handling it could result in serious injury or death.

    Required Items

    • Wire strippers
    • Length of insulated copper wire
    • Electrical tape
    • Flathead screwdriver with rubber or insulated handle
    • Multimeter with alligator clips
    • Wire snips
    • Needle-nosed pliers
    • Soldering iron and solder flux
    • Replacement capacitors or tubes

    About the Author

    Jeff Grundy has been writing computer-related articles and tutorials since 1995. Since that time, Grundy has written many guides to using various applications that are published on numerous how-to and tutorial sites. Born and raised in South Georgia, Grundy holds a Master of Science degree in mathematics from the Georgia Institute of Technology.

    Photo Credits

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