In a report, published in the November 1919 issue of Wireless World of a British Association Meeting, a paper entitled 'A trigger-relay utilizing three-electrode thermionic vacuum tubes' by W H Eccles and F W Jordan was recorded. This is the famous Eccles-Jordan flip-flop, without which computers would not exist.
In a well-known method of using a triode for the amplification of wireless signals an inductive coil is placed in the filament-to-anode circuit, and another coil magnetically coupled with this is introduced into the filament-to-grid circuit. This 'back-coupling' as it is sometimes conveniently called, if it is arranged in the right sense, greatly exalts the magnification produced by the tube in any alternating EMF applied to the grid; for the induced EMF passed back to the grid is in correct phase relation to add directly to the original alternating EMF applied there. If instead of using inductive retroaction of this kind we attempt to use resistance back-coupling, then the retroactive EMF applied to the grid is exactly opposite in phase to the original alternating EMF, and the amplifying action of the triode is reduced. Since, however, one triode can produce opposition in phase in the manner indicated it is clear that two or any even number of similar triode-circuits arranged in cascade can produce agreement in phase.
Hence we conclude that retroactive amplification can be obtained by effecting a back-coupling to the first grid from the second, fourth, and so on, anode circuit of a set of triodes arranged in an ohmically-coupled cascade.
It is possible to take advantage of the fact above stated for obtaining various types of continuously-acting relay. The paper described a one-stroke relay, which, when operated by a small triggering electrical impulse, undergoes great changes in regard to its electrical equilibrium, and then remains in the new condition until re-set.