Parts of a capacitor.

As shown here, a capacitor consists of two or more parallel conductive (metal) plates which are not connected or touching each other, but are electrically separated either by air or by the insulating layer between a capacitor’s plates.

This material is called the dielectric. Transistor radios use a variety of capacitors including very small fixed value capacitors used in resonance and audio circuits. Capacitors temporarily store electrical energy, smoothing out unwanted voltage variations within circuits. They also “isolate” AC voltage, such as RF and IF signals from DC current within the circuit.

In fixed capacitors, the dielectric is a good insulating material such as waxed paper, mica, ceramic, or plastic. A liquid gel--often called the electrolyte is used in electrolytic capacitors. It is this gel that eventually dries out, silencing our prized possessions.

Variable capacitors are used in transistor radios to adjust tuned circuits. In large variable capacitors air is the electrolyte. In small tuning caps are usually thin, flexible plastic.

A third very common component found in radios is the electrolytic capacitor. These deteriorate over time and are frequently the cause of dead or poorly performing sets. Many hobbyists replace the electrolytics in a process called recapping.

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