connection with the bus bar so the bus may be, quite safely, at any (EHT) voltage with respect to the instrumentation. Instrumentation magnetic amplifiers are commonly found on space craft where a clean electromagnetic environment is highly desirable. The German Kriegsmarine made extensive use of the magnetic amplifiers. They were used for the master stable element systems, for slow moving transmission for controlling guns, directors and rangefinders and train and elevation controls. Magnetic amplifiers were used in aircraft systems (avionics) before the advent of high reliability semiconductors. They were important in implementing early autoland systems and Concorde made use of the technology for the control of its engine air intakes before development of a system using digital electronics. Magnetic amplifiers were used in stabilizer controls of V2 rockets. Usage in computing Magnetic amplifiers were widely studied during the 1950s as a potential switching element for mainframe computers. Like transistors, mag amps were somewhat smaller than the typical vacuum tube, and had the significant advantage that they were not subject to "burning out" and thus had dramatically lower maintenance requirements. Another advantage is that a single mag amp could be used to sum several inputs in a single core, which was useful in the arithmetic logic unit (ALU) as it could greatly reduce the component count. Custom tubes could do the same, but transistors could not, so the mag amp was able to combine the advantages of tubes and transistors in an era when the latter were expensive and unreliable. The principles of magnetic amplifiers were applied non linearly to create magnetic digital logic gates. That era was short, lasting from the mid-1950s to about 1960, when new fabrication techniques produced great improvements in transistors and dramatically lowered their cost. Only one large-scale mag amp machine was put into production, the UNIVAC Solid State, but a number of contemporary late-1950s/early-1960s computers used the technology, like the Ferranti Sirius, Ferranti Orion and the English Electric KDF9, or the one-off MAGSTEC. History Early development A voltage source and a series connected variable resistor may be regarded as a direct current signal source for a low resistance load such as the control coil of a saturable reactor which amplifies the signal. Thus, in principle, a saturable reactor is already an amplifier, although before 20th century they were used for simple tasks, such as controlling lighting and electrical machinery as early as 1885. In 1904