What Are Tubular Axial Capacitors?

The Function of Capacitors

• Capacitors store an electrical charge, but unlike a battery, they cannot produce electricity on their own. They are used in a wide variety of electronic circuits. In power supplies, they help smooth out alternating current (AC) ripple in rectifier circuits. In oscillators, they are a factor in determining the frequency of oscillations. They block the passage of direct current (DC), while allowing AC signals to pass through. You may even find a capacitor in your stereo speaker system, separating high frequencies and passing them to cabinets' tweeters.

Tubular Capacitor Construction

• Capacitors work by having two conductive plates separated by an insulating material. Energy is stored in an electrostatic field created between the two plates. In the case of tubular axial capacitors, the "plates" are a metal foil with an insulating material between them, all of which are rolled together like a jelly roll. Tubular axial capacitors typically have a polypropylene film dielectric and aluminum foil electrode. The tubular outside body is wrapped with a polyester film and the ends are sealed with epoxy resin.

Capacitors in Circuits

• In today's electronics, integrated circuits and supporting components, such as resistors and capacitors, are often very small and are soldered directly onto printed circuit boards. In the early days of radio, however, components were much larger. This is in part due to the fact that these appliances used vacuum tubes, which are big, bulky, hot and require much higher voltages to operate than modern transistors and integrated circuits. Components such as resistors, coils and capacitors were often connected between tubes and other components using the long wire leads that exit them, soldering the leads to pins on tube sockets and lugs on terminal strips as tie points. As its name implies, tubular axial capacitors have a tube-like body with a wire lead extending out of each end, like the axle on a vehicle.

Ratings

• Vacuum tube appliances generate a lot of heat and require voltages in the hundreds of volts. Operating in these conditions requires capacitors to be capable of handling high voltages and high temperatures, and tubular axial capacitors are used in these situations. Common voltage rating for these capacitors are 600 and 1,000 volts. Voltage ratings and capacitance values (in microfarads) are typically printed on the tubular case.