Patent GB-359967-A (GB)
Title: Radio-electric musical instrument with keyboard and thermionic valves
IPC: G10H5/02
Filed: 1930-07-25
Abstract: 359,967. Electrical musical instruments ; thermionic valves. COUPLEUX, E. E., 24, Rue Esquermoise, Lille, and GIVELET, J. A. M. V. DE P., 24, Rue Bois-de-Vent, Paris, both in France. July 25, 1930, No. 22512. Convention date, July 26, 1929. [Class 88 (ii).] A polyphonic keyboard instrument with thermionic valve oscillatory circuits comprises means for reducing the amplitudes of the harmonics (though harmonics of small amplitude may remain, being utilized for varying the timbre), and means such as filters for suppressing interference beats between harmonics and between harmonics and fundamentals. The amplitudes of the harmonics may be reduced by selecting the ratio between selfinduction and capacity ; by adopting a suitable coupling between plate and grid circuits; by suitably polarizing the grid ; by choosing suitable heating and plate potentials; or, Fig. 12 (not shown), by collecting the oscillating currents inductively and tuning the inductive circuits to the corresponding notes. Valves of high internal resistance also may be used. For suppressing the beats, a filter, consisting of one or more capacities in parallel with one or more self-inductances, is preferably provided for each octave. The number of parts required may be reduced by the use of multiple valves and frequency doublers. Timbre is varied by varying the ratio of self-induction to capacity (product remaining constant to preserve pitch) ; by varying the grid polarization by a potentiometer; by varying the filter elements ; by putting notes imperceptibly out of tune, obtaining beats between harmonics capable of affecting timbre; by using weak fundamental notes as harmonics to other notes. Separate loud-speakers may be used for high and low notes. Tremolo may be obtained, Fig. 11 (not shown), by rotating a solid, laminated, cased, or wound core between the arms of a wound magnet as in Specification 342,952. In Fig. 1, the grid circuits 11 .. of the valves L1 .. of one octave are connected to the same potentiometer 3 through the keys T1 .. , and the plate circuits 21 .. are connected through a filter 4, 5 to the primary 6 of a transformer 10 connected to the amplifier 8 and loud-speaker 9. The circuits of the valves L<1>1 .. of the second octave are similarly connected, the relative loudness of the octaves being varied by varying the coupling of the primaries 6 .., or by a variable resistance 11. Tuning is effected by a knob 13, Fig. 2, above the key 14, controlling a laminated core 12 movable either within an impedance coil or between the arms of a magnet with coil. Fig. 4 (not shown) illustrates the switch arrangements for introducing alternative capacities and inductances simultaneously into the valve circuits for varying the timbre. A single valve may be used for a note and its sharp, Figs. 5 and 6 (not shown). In Fig. 7 the same valves and oscillating circuits are used for different octaves, the keys T1 .. of the lower octave being directly connected to the amplifier 25 and loud-speaker 26, while the keys T1<SP>1> .. of the upper octave are connected through a frequency doubler 23 and transformers 24, 27. Fig. 8 shows a multiple valve with a single central filament 28, and the grid and plate sets 291, 301 .. connected to the circuits 11, 21 .. controlled by the keys T1... Or the grid or the plate may be the single electrode. In Fig. 9 (not shown), the filament is doubled back to avoid buzzing produced by alternating current, and metallic screens are placed in the valve between the grid and plate sets. In Fig. 10 (not shown), individual filaments are connected in shunt, like rungs of a ladder, between two supports.