Categories of exhibits
Power vacuum tube 13E1
Exhibit no. 956
Electromagnets in magnetic sector analyzers produce a magnetic field when an electric current passes through them. The stability of magnet current is of considerable importance, particularly for mass measurements made at high resolving power. In the pre-semiconductor era of electronics, power vacuum tubes were used in circuits powering the electromagnets.
The exhibit is a vacuum tube 13E1 from the MS902 double-focusing mass spectrometer manufactured by AEI Scientific Apparatus Ltd. in 1969. The MS902 magnet had two coils of 330 ohms each connected in series. It was powered by a unit producing a smoothed direct current of 800 mA at 800V. Before applying to the magnet coils, the current passed through a magnet regulator circuit with three 13E1 beam tetrodes. They were used as series valves, sharing the magnet current entering from the power unit. When one of the tubes failed, all three had to be replaced. While the price of one tube in 1969 was GBP19, in 1985 it was GBP 226. Type 13E1 beam tetrode had a double cathode, with an option to heat only one part of it. The tube was first introduced in 1955.
