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  2. Western Electric hand telephone sets - Wikipedia

    en.wikipedia.org/wiki/Western_Electric_hand...

    The Western Electric hand telephone sets are a series of telephones that were produced from 1927 by the Western Electric Company for the American Telephone and Telegraph Company (AT&T) and the Bell System. The series features the mouthpiece (transmitter) and the earpiece (receiver) combined into a hand-held unit, originally named a hand ...

  3. Radio receiver - Wikipedia

    en.wikipedia.org/wiki/Radio_receiver

    An AV or Stereo receiver (in context often just called a receiver) is a component in a hi-fi or home theatre system combining a radio and audio amplifier in one unit that connects to the speakers and often to other input and output components (e.g. turntable, television, tape deck, and CD and DVD players)

  4. Automatic gain control - Wikipedia

    en.wikipedia.org/wiki/Automatic_gain_control

    Schematic of an AGC used in the analog telephone network; the feedback from output level to gain is effected via a Vactrol resistive opto-isolator.. Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the input.

  5. Sound-powered telephone - Wikipedia

    en.wikipedia.org/wiki/Sound-powered_telephone

    Modern emergency telephone powered by sound alone. A sound-powered telephone is a communication device that allows users to talk to each other with the use of a handset, similar to a conventional telephone, but without the use of external power. This technology has been used since at least 1944 [ 1 ] for both routine and emergency communication ...

  6. Trimline telephone - Wikipedia

    en.wikipedia.org/wiki/Trimline_telephone

    Early foreign made Trimline, December 1986. 90s Trimline phone made by Lucent/Philips and branded AT&T. The Trimline telephone is a series of telephones that was produced by Western Electric, the manufacturing unit of the Bell System. These telephones were first introduced in 1965 and are formally referred to as the No. 220 Hand Telephone Sets.

  7. History of radio - Wikipedia

    en.wikipedia.org/wiki/History_of_radio

    In 1929 a new screen grid tube called UY-224 was introduced, an amplifier designed to operate directly on alternating current. [57] A problem with the early radios was fading stations and fluctuating volume. The invention of the superheterodyne receiver solved this problem, and the first radios with a heterodyne radio receiver went for sale in ...