GB312336A - Improvement in protective circuit for vacuum tubes - Google Patents

Abstract

312,336. Standard Telephones & Cables, Ltd., (Assignees of Schelleng, J. C.). May 26, 1928, [Convention date]. Thermionic amplifiers. - In a high-powered generating installation a protective switch in the plate supply is opened by a relatively inexpensive relay located in the low-voltage filament circuit, and a visual indication is simultaneously given of any particular amplifier which is being over-run. The drawing shows two amplifiers 1, 2 fed in push-pull from a high-frequency source 5. Grid bias is supplied from a source 21 through parallel resistances 22, 23 and filter circuits 24. The safeguarding relays 60, 61 are inserted in the filament-supply circuit fed from a source 16, the windings of the relays being so arranged that they are insensitive to changes in the actual filament current, through any excess in the normal plate current (which flows through the windings in parallel) breaks one or other of the contacts 43, 43<1> and so opens a circuit-breaker 33 on the primary side of a transformer 66 feeding the rectifier 30 which supplies high-tension to the plates of the amplifiers 1, 2. The holding-relay for the circuitbreaker 33 is normally energized from a source 34 through relays 35, 35<1>, which are in series with -the filament relays 60, 61, and are therefore operated when any dangerous increase in plate current takes place. As one or other of the relays 35, 35<1> falls, it energizes a lamp 51, 51<1> to indicate the particular amplifier at fault. The relays 35, 35' are re-set through a push-button 37, source 36, and relay 38.