GB319695A - Improvements in and relating to volume control apparatus for combined phonographs and radio receivers - Google Patents

Abstract

319,695. British Thomson-Houston Co., Ltd., (Assignees of Whelan, D. 0.). Sept. 26, 1928, [Convention date]. Receiving-sets combined with phonographs ; thermionic amplifiers and detectors.-In a combined radio-phonograph apparatus, volume control, either for radio reception or phonographic reproduction, is effected by a device comprising two rheostats actuated by a single knob- The device comprises two mechanically coupled potentiometers 26, 22, Fig. 2, potentiometer 22 being in the aerial circuit so that any or all of the voltage drop across -the potentiometer is impressed on the grid of valve 5. A suitable power supply device 15 provides filament current and plate voltage. The detector valve 9 has an indirectly-heated cathode with independent filament supply 17 ; valve 11 also has a separate supply 18, while the three radio-frequency valves 5, 6, 7 and the low-frequency valve 10 have a common supply 16. Potentiometer 26 is connected across the pick-up coil 25, the output 27 being led to transformer 12 through the switch 29, operated by a lever 30. A second switch 31 renders the radio-frequency or detector valves inoperative when lever 30 is set at " Phonograph." In the construction shown in Figs. 2 and 3, circular resistance strips 37, 38 are fitted in insulating discs 35, 36, which have bearings 39 mounted on the shaft 40; the discs are aligned by spaces 42 and bolts 43, an insulating coupling 44 being inserted between the potentiometers. For panel mounting, a bent strip frame 49, held at its ends by bolts 43, secures the unit to the panel 50. Except for the resistance strips, the components of the two potentiometers are interchangeable.