plastic plunger positioned above a pair of levers connected in a spring-loaded yoke that operated the hook switch; pressing the plungers down, end the call, and place the phone on hook. The plastic face of the dial under and surrounding the finger wheel is a part of the dial assembly and is exposed through the circular opening in the housing. On the bottom, the flat steel plate of the chassis is exposed. The handset cord exits from the left side of the housing at the base, and the line cord emerges from the rear at the base. Internally, the phone contains circuitry composed of many passive electrical, electronic, and mechanical components. The set needs no separate power supply as it is received transmitter current from the telephone line; when it is on hook and not ringing, it uses no power, as the ringer is isolated with a capacitor from the direct current (DC) potential of the local loop. The most complex part is the rotary dial mechanism, an assembly of gears, cams, springs, and electrical contacts which mechanically generate a timed train of line loop-break pulses when the dial finger wheel is released after rotation. During the period of dial rotation, the receiver is shunted to avoid hearing the dial pulses. The electromechanical ringer consists of two bell gongs of slightly different dimensions to produce different pitches and a striker between them that is driven by a solenoid; when the solenoid is energized by alternating (AC) ringing current, typically about at , it strikes the two gongs alternately, producing a distinctive effect of two superimposed sounds. In telephones with a ringer loudness control, one gong is mounted off-center on the loudness control wheel; turning the wheel moves the gong toward (quieter) or away (louder) from the striker. The model 500 ringer was fairly loud and could be heard a few rooms away. The ringer could not be turned off by the user but could be disabled in the wiring. The model 500 telephone was designed for long service life. Telephones in the Bell System were owned by and leased from the telephone company, which was responsible for keeping them in good repair. The phones were rugged and reliable and intended to last for decades with little maintenance. The 1940s-era technology of the 500 made extensive use of metal components and point-to-point wiring, and most components were modular and easy to