File:German Post Office subscription radio receiver 1923.jpg

English: German man in 1923 listening to a subscription radio receiver provided by the German post office. AM radio broadcasting in Germany began in August 1922 as a subscription service offered by the German Post Office. For a monthly fee the Post Office provided this vacuum tube radio receiving apparatus. It only received one station, on 4000 meters (75 kHz) broadcast by a network of 12 10 kW transmitters throughout Germany run by the Post Office, with content provided by the Berlin Telegraph Agency, Eildienst, GmbH. It's distinctive feature was its ease of use. At a time when radio receivers were cumbersome devices with many knobs and dials that had to be adjusted correctly and required several batteries to work, this set ran off household current and had only a single adjustment knob (center), a vernier tuning knob to keep it on frequency. Taking the earphones off the hook turned on the power and warmed up the filaments. The vernier adjustment could only adjust the frequency by 2%, to meet the Post Office requirement that the receiver not be able to pick up any other stations, preserving its monopoly over broadcasting in Germany.

Caption:"Complete broadcast receiving equipment as installed by the German Post Office. The instrument on the left provides filament heating and plate current from the DC mains. The tuner is in the center and the instruments on the right are double and single LF amplifiers"