The vacuum tube was the only amplifying device ( besides specialized power devices such as the magnetic amplifier and amplidyne ) for 40 years, and dominated electronics until 1947, when the first transistor, the BJT, was invented.
32.
E . F . W . Alexanderson of the General Electric Company applied for his magnetic amplifier patent in 1912 and was responsible for the development of a system of transoceanic radio communications, using continuous wave transmission over great distances.
33.
A permanent magnet high frequency generator, directly coupled to the exciter shaft, acts as a pilot exciter and supplies the exciter field via a power stage magnetic amplifier which may be regulated either by manual control or by the automatic voltage regulator.
34.
As the prices of transistors dropped, Ken Johnson, an engineer at the lab, proposed a new type of transistor-based logic that followed the same conventions as the magnetic amplifiers, namely that binary logic was based on well known currents instead of voltages.
35.
However, Rubin began working on a completely novel system with greatly improved sensitivity, and by early 1956, he had produced a prototype second-harmonic magnetic amplifier-type core balance system ( South African Patent No . 2268 / 56 and Australian Patent No . 218360 ).
