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We receive many emails about technical troubles with old classic tube CB's. The most common complaint is "my tube CB radio hums or buzzes through the speaker" We also realize many of you have no experience with restoring old electronics. Many visitors are not technical or "radio people" but individuals from all walks of life who share a common interest in locating & obtaining a favorite old CB classic from years ago. Retrocom highly encourages this behavior and as a service offers this information regarding one of the most frequent failures in an old transceiver.
Aging Electrolytic Capacitors
Most tube CB radios have a relatively simple power supply arrangement consisting of a power transformer, rectifier & filter section, that increases voltage from your outlets 117AC line voltage to a higher value DC voltage which powers the various transmit and receive sections of the radio. Over the course of time age, previous heating, and chemical action has an effect of drying out the electrolytic capacitors in the CB's power supply. The result is a loudly buzzing or humming set and if neglected can result in damage to the rectifiers or power transformer. There may or may not be any physical indications of a failure. Sometime there will be a bulging or tan deposits visible. The capacitors are actually multi-sectioned, consisting of several individual capacitors all sharing a common housing, and usually mounted vertically on the topside of the chassis. They look like a large aluminum or colored cardboard covered cylinder. Finding an exact replacement may be very expensive, but research on the internet will yield results, as many of the type of caps used in the old CB's are still being used in new & restored tube type audio amplifiers. A less expensive alternative to total replacement is the installation of separate modern axial lead caps of the appropriate values. This type of cap is more readily available and their small size allows them to be hidden under the chassis where there is usually enough room to connect the new caps to existing circuits. It is best to totally disconnect the old capacitor sections because we have seen these components fail in a shorted mode, this would render your repair ineffective. Make sure you discharge the power supply to chassis ground before replacing any components. Replacing the aging electrolytic caps can insure many more enjoyable years of life from your CB classic!
Caution : Before attempting any repair on a tube type CB beware that there are many exposed circuits, wires & terminals that may remain charged with hundreds of volts. Shock, burn or electrocution could result without taking proper precautions. If you are unsure as how to proceed, please seek the advice of a professional electronic technician.