| 摘要 |
879,998. Valve amplifying circuits; gain control. HAZELTINE CORPORATION. April 6, 1960 [May 6, 1959], No. 12197/60. Classes 40(5) and 40(6) [Also in Groups XL(a) and XL(b)] An amplifier gives two outputs, one of fixed and the other of variable gain. Signals are applied to the grid 13 of a beam valve which comprises screen-grid 25, beam deflection electrodes 16a, b and two anodes 15a, b respectively. The proportion of the electron beam falling upon each of the anodes can be varied by varying the bias upon deflection electrodes 16a, b by means of ganged potentiometers 18a, b and an adjustable output is taken from anode 15b via terminal 23. The circuits of the two anodes comprise equal resistors 19a, b and are bridged by a centretapped resistor 20 from the centre of which is taken an output which does not vary as the potentiometers 18a, b are varied. The arrangement is used in a television receiver as video amplifier; the variable output being takeu to the picture tube as a signal of variable contrast while the fixed output is applied to the synchronizing circuits. |
