POWER VALVES

Radio Record, Volume I, Issue 16, 4 November 1927, Page 14

POWER VALVES

CORRECT USE. Tower valves are power handlers, not power ptoducers as many think. . Of itself, a power valve will not produce more volume than a non-power valve. The value of a power valve lies in the fact that its design. permits it to handle greater volume without distortion. Most receiving sets are capable of delivering more volume to the last audio yalve than can ke handled without distortion by the usual types of amplifying valves. This is where the power valve is needed-in the last audio stagewhere it can receive the volume developed in the earlier stages of tlie set and pass it on, amplified but undistorted, to the loudspeaker, Electrical Characteristics. The electrical characteristics of power valves are quite different from those of the customary amplifying valves. Power valves consume more B battery current and they require greater C battery voltage. The wrong C voltage robs the power valve of its ability to handle greater volume without distortion. In addition, if the C voltage is too low the B current consumed by the valve is multiplied many fold, which rapidly exhausts the B battery. Merely substituting a power valve for some other valve in the last audio stage of a receiver will not bring about any noticeable improvement in reception. Provision must he made to allow placing the correct C voltage on the grid of the power valve, and a greater B battery voltage can be employed.