The amplifier on this telephone was invented in Seattle by P.J. Hackett and produced by the Universal High Power Telephone Company. Hackett was an assistant to William Dubilier who created the first successful wireless telephone in 1910. After Dubilier left Seattle, Hackett continued to work on microphones and amplifiers that could handle the heavy currents of radio and landline telephones before the advent of vacuum-tube amplifiers. His designs were manufactured by Universal High Power Telephone Company which operated in Seattle from about 1910-1933. This particular telephone was used by Seattle City Light. The receiver was made by Stromberg-Carlson Telephone Manufacturers of Chicago