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DC-34 Holders 1690 KC to 4400 KC steps of 10 KC ea. .. .$1.19

Some of these earlier sets used a constant* voltage transformer to offset the degradation in performance at reduced input voltage. These transformers were manufactured by Sola and were of the saturable reactor type, While they were used primarily to compensate for primary voltage variations, they also provide good regulation with changing load.

The RA-109 chassis, used in many sets marketed in 1951, is typical of those using the constant-voltage transformer, Although very fine sets, housed in good cabinets, many are being junked today and a little searching will dig them out.

The schematic diagram of the regulated supply used in the I iA 109 chassis is shown in Fig. I. Both the rectifier filament and the high voltage secondary windings of the transformer are regulated. The inductance of I he high voltage secondary winding is tuned to resonance by the 2 mfd capacitor. Because of this resonant condition, a high circulating current flows in the winding, causing this section of the core to become saturated. Because of Ibis saturation, the secondary voltage is relatively constant over a wide range of load and primary voltage variations.

Specifically, this transformer is designed to maintain the dc voltage output constant within ±2¥ for line voltage variations of ±10% from the rated 117 volts. This insures stable dc output for line voltages ranging between 105 and 129 volts. Only one precaution is required in amateur use of this supply. The nominal 2 mfd capacitor used to tune the secondary is hand selected in production to match the transformer used, Do not change the value of this capacitor or much of the regulating effect will be lost.

This particular supply is rated at 362 volts at 210 ma and no undue heating occurs at this load. This salvage power supply is a low cost answer to the critical voltage regulation problems encountered in many amateur applications. . . , . W4WKM

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