US2242983A - Photoelectric phonograph - Google Patents

Description

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. www? H H May 20, 1941 M. L. THOMPSON ruoToELacTRrc PHouoGRAPH Filed Dec. 13, 1940 Patented May 2G, 194i UNT. S

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rnoroaeacrarc rnonoeaern Applica-tien December i3, 1940, Serial No. 370,083

l1 Claims.

This invention relates to radio-phonograph combinations employing photoelectric pickup devices, 'and more particularly to the energization of the light sources of said photoelectric devices. The improved light source energizing means of the present invention may be advantageously employed in connection With photoelectric sound reproducing systems in general, but `is particularly adapted for use with photoelectric pickups of the type employed in the reproduction of mechanical (e. g. disc) recordings. A photoelectric pickup device of this type is disclosed, for example, in the -copendng application of E. O. Thompson, Serial No. 357,322, filed September 18, 1940.

Photoelectric phonograph pickup devices for use with mechanical recordings usually comprise a light source, a mechanical system for modulating or fluctuating the beam of light from said source in accordance with the recorded sound, and a photoelectric cell which is exposed to the modulated light beam and which, under the influence of the light, functions to generate an electrical signal whose waveform is proportional to the fluctuations in said beam of light. Since the photoelectric cell responds to minute variations in the level of illumination, it is necessary to employ a light source which provides an illumination substantially free of variations in intensity, particularly of cyclical variations occurring fat audio frequencies. A simple way of securing such an even illumination is to operate the lamp from a direct current source, for example from a battery, or from an alternating current power pack comprising rectier and lyter means. Neither of these eXpedients is convenient, however, particularly Where the equipment is to be employed in radio-phonographs intended for home use.

'Ihe principal object of the present invention is to provide novel and convenient means for energizing the lamp of the photoelectric pickup in a radio-phonograph combination employing such a pickup.

In accordance with this invention-it is proposed to employ the oscillator circuits of the radio receiver as a source of high frequency current for heating the filament of the lamp to incandescence. If the oscillator is adjusted to operate at a super-audible frequency, e. g. at radio frequency, no audible signal can be generated by the photoelectric cell since the variations in illumination provided by the lamp will occur at a frequency beyond audibility,- specifically at double the frequency of the current supplied by the oscillator. Moreover, .at high frequencies, the actual variation in illumination will be extremely small .due to the thermal lag of the filament winding as compared to the period of the high frequency heatingv curn rent.

Another object of the invention is to provide a novel circuit arrangement whereby the energy available from the oscillator is increased during the operation of the phonograph.

Other objects and features of the invention will appear hereinafter.

The invention may best be understood by reference to the accompanying drawing, the single figure of which is a diagrammatic illustration of a radio-phonograph combination embodying the invention.

, Referring to the drawing, the phonograph- ,to the mirror by means of the crank arm 8 causes the mirror to be vibrated about the central axis 9 which extends perpendicularly to the plane of the record. The lamp and cell Iare preierably so adjusted with respect to the mirror that the beam of light is normally half on and half off the cell 4, so that when the pickup is placed on a record, the undulations of the reccrd grooves will cause the illuminated area of the cell to vary in accordance with the said undulations. rIhe electrical output of the photoelectric cell 4 may be applied to a Suitable amplier by way of the lead wires I0, while the lamp 2 may be energized from a suitable current source by way of the lead wires I I.

The radio receiving apparatus illustrated in Fig. 1 comprises a radio frequency amplifier I2, first detector I3, oscillator means comprising the vacuum tube V1 and associated tuned circuits, intermediate frequency amplifier I4, second detector I5, audio frequency amplifier I 5, loudspeaker L. S., and a power supply source I'I. In the specific embodiment shown, a four-position Wave band switch is provided for making all connections necessary for selective operation of the apparatus as a phonograph, as a radio with push employed to give a band spread effect. Vshortvrave position of the gang'switch, as well as in the other two radio positions-the oscillator button` control, or with manual control in either the broadcast or short wave bands. These posi tions of the wave band switch are designated by the Band indicator having positions lettered Phono, P. B, B. C., and S. W. respectively.V

In the short wave position (S. W.) of the band switch, the oscillator tube V1 is connected,y by way of the condenser i3 and gang switch section S1, to the short wave coil I9 and the variable tuning condenser 26. rThe condenser 2i is connected in series with the variable condenser 23" in this position of the band switch and may be In the signal may be supplied to the first'deteetor stage I3 by way of the lead 22 and the v'gang switch section Sz. Any of the conventional mixing circuits may be employed.

' In the manual broadcast position'(B. C.) of the band switch, the'oscillator tube is connected to the` broadcast coil 23 and the variable tuning condenser 2i). The coil 23 may be shunted by a parallel trimmer condenser as shown, while the series trimmer condenser 23 may be inserted serially in the variable tuning condenser circuit as is well understood in the art.

In the push button position, the coil 23 and its shunt trimmer condenser is retained in the circuit, but any one of the preadjusted individu ally selectable trimmer oondensers 25, 26 or 21 may be substituted for the variable tuning con-v denser 20.' p In any of the three positions of the wave band switch above referred to, the oscillator tube V1 may be supplied with plate current from the Bv supply Il through a shunt feed system comprising the voltage dropping resistor 28, the R. F.

coil 33 to the lamp 2 in the Phono position of the gang switch. The coupling between the coils 23 and 33 should be adjusted to ensure an efficient transfer of energy from the oscillator V1 to the lamp 2. Inductive coupling between the coils 23 and 33 is indicated by the symbol M.

Although, as indicated above, it is possible to utilizeone of the receiver coils I3 or 23 as a part of the oscillator circuit when the tube V1 is used to supply heating current to the incandescent lamp 2, it will be understood that where desired a separate `coil may be provided for exclusive use in connection with the phonograph operation of the system. Although heating current frequencies have been found to be not critical, frequencies of about 1800 kilocycles have been used for this purpose, since such frequencies are conveniently obtained when shunting the regular broadcast band oscillator coil 23 with a small trimmer' condenser 32, as shown.

`Since the power requirement of the lanrp 2 is relatively high as comparedfto the normal power output of an oscillator' employed in its usual capacity in adetector-oscillator circuit, it may 'benecessa-ry to supplyto the oscillator a substantiaily greater than normal plate voltage.

three radio positions of section Se of the band switch, the resistor 28 will be inserted serially in the lead from the plate supply source i1 to the anode of the tube V1. It may further be noted that in the above-mentioned three radio positions, the output of the second detector i5 is connected to the input of the audio frequency ampliier le, and the cathode or cathodes of the one or more intermediate frequency amplifier tubes V2 are connected to chassis or ground through the gang switch section S7.

In the phonograph position of the band switch (shown) the oscillator tube remains connected tol the broadcast coil 23, the preadjusted tuning con-` tankV circuit 23, 32 by means of the coil 3-3 and" thelamp vleads il. The gang switch section S4, it will be noted, connects the ungrounded end of This may be accomplished in theV circuit illustratecl by short circuiting the voltage dropping resistor 23-by means ofthe gang' switch section Se. Thus, the oscillator V1 may be suppiied with the full output voltage of' the B supply Il, since there will be only a negligible direct current vole tage drop in the R. F. choke 29. the B supply l1 be not overloaded by the unY usually heavy oscillator load, it may be desirable to kdecrease the current consumption of those radio receiver circuits notdirectly involved when the apparatus is employed as a phonograph. This may be effected, for example, by open-circuiting the plate and screenV circuits of the radio and intermediate frequency amplifiers and of the firstdetect'or. In the illustration, by way of example, they intermediate frequency'amplifiery tube V1 is provided with'the switch S7 in its cathode* circuit. This switch is closed in the three radio positions' of the lwave 'band switch, but is open in the Phono position' thereof.A This arrangement makes it possible to supply adequate power to the oscillator tube witho'utr'esorting to power supply systems having 'greater than normalY power output capacity.

Insome instances it may be found expedient to omit the gang switch'section S4 entirely, thereby sin'iplifyingA the design fof the gang switch. In this case the connectionV eected by the switch S4 as illustrated in the drawing would be made permanent. Under these" conditions the lamp 2 Vremains a load'on the oscillator tube V1 during voltagereductio may be of such an order that,

during radio reception,- thevlamp 2 is so feebly eircitedthat it fails to glow, or just` barely glows;

The switch Sa-may then be regarded as a means for increasing the radio frequency energy sup-- plied t the lamp 2 duringphoncgraph operation.

oscillator tubeshouldY beY selected which is capable of generating sumcient high frequency' In order that power to satisfactorily excite the lamp in the photoelectric pickup head. A type 7B5 pentode which is rated at 3.4 Watts when supplied with 250 volts at the plate has been found capable of driving a lamp rated at 3.3 volts and 0.6 ampere vrepresenting a power consumption of about 2 watts.` Lamps containing an atmosphere of an inert gas, such as argon, for improved filament life, have been found satisfactory for use in photoelectric pickups vof the type referred to herein. Where the `lamp is mounted in thepickup head, and, therefore, may be subjected to some vibration, it is desirable to select lamps having filaments designed and mounted in such a manner as to be free from microphonics.

'Ihe electrical output ofthe photoelectric cell maybe applied directly to the input of the audio frequency amplier I6 by Way of the gang switch section S5, or, if desired, a preamplifier 34 may be inserted ahead of the amplifier I6. pre-amplifier for use with amplitude-responsive photoelectric pickups, when used in combination with constant velocity recordings, is fully described in a copending application of M. L. Thompson and E. O. Thompson, Serial No. 361,968, lled October 19, 1940.

The herein-disclosed embodiment of the invention is illustrative of the novel features thereof, and is not to be taken as limiting the invention. It will be apparent to those skilled in the art that further embodiments and modifications of the invention are possible within the scope of the appended claims.

I claim:

1. In a radio-phonograph combination, a radio receiver of the superheterodyne type including a local oscillator, an electro-optical phonograph pickup device including an electric lamp, switching means for selectively eiecting radio or phonograph operation, and means operable by said switching means for coupling said lamp to said oscillator during phonograph operation, thereby to supply energy from said oscillator to said lamp.

2. In a radio-phonograph combination, a radio receiver circuit of the superheterodyne type including a high frequency vacuum tube oscillator circuit, a photoelectric phonograph pickup device including a light source comprising an electric lamp, means for selectively effecting radio or phonograph operation, and means for supplying energy from said oscillator circuit to said lamp during phonograph operation.

3. In a radio-phonograph combination, a radio receiver of the superheterodyne type including a local oscillator, an electro-optical phonograph pickup deviceincluding an electric lamp, a multiposition switch, means including contacts on said switch for selectively effecting radio r phonograph operation, and means including additional contacts on said switch for coupling said lamp to said oscillator during phonograph operation, thereby to supply energy from said oscillator to said lamp.

4. In a radio-phonograph combination, a radio receiver of the superheterodyne type including a local oscillator having a tank circuit, an electrooptical phonograph pickup device including an electric lamp, an energy supply circuit for said lamp coupled to said tank circuit, switching means for selectively effecting radio or phonograph operation, and means controlled by said switching means for rendering said supply circuit operative only during phonograph operation, thereby to supply energy from said oscillator to said lamp.

A suitable 5. In a radio-phonograph combination, a multi-band radio receiver. of the superheterodyne type including a local oscillator, an electro-optical phonograph pickup device including an electric lamp, a multi-position switch 4for operating said receiver in diierent frequency bands and for selectively eiecting radio or phonographV operation, and means including contactsonsaid switch for coupling said lamp to said oscillator during phonograph operation, thereby to supply energy from said oscillator to said lamp.

6. In a radio-phonograph combination,` a multi-band radio receiver circuit of the superheterodyne type, a multi-band vacuum tube oscillator circuit for said receiver, said oscillator circuit comprising a plurality of tunable tank circuits capable of being tuned over a plurality of wavebands, switching means for selectively effecting radio or phonograph operation and for selecting any one of said tank circuits to enable said radio receiver to be tuned over a desired one of said wave-bands, a photoelectric phonograph pickup device including a light source comp-rising an electric lamp, and means for operating said oscillator circuit at a frequency whose second harmonic is beyond the range of audibility and for supplying energy from the oscillator circuit to said lamp during phonograph operation.

7. In a radio-phonograph combination, a radio receiver circuit of the superheterodyne type including a high frequency vacuum tube oscillator circuit, a photoelectric phonograph pickup device including a light source comprising an electric lamp, means for selectively eiecting radio or phonograph operation, means for supplying energy from said oscillator circuit to said lamp during phonograph operation, and means for supplying greater-than-normal anode voltage to said oscillator tube when the oscillator circuit is utilized to excite said lamp during phonograph operation.

8. In a radio-phonograph combination, a radio receiver circuit of the-superheterodyne type including vacuum tube amplifiers and a high frequency vacuum tube oscillator circuit, a source of limited energy supply for said vacuum tube oscillator and for the vacuum tube amplifiers in said receiver circuit, a photoelectric phonograph pickup device including a light source consisting of an electric lamp, means for selectively electing radio or phonograph operation, means for supplying energy from said oscillator circuit to said lamp during phonograph operation, and

means for opening the space current circuits of one or more of those vacuum tubes which function solely in the radio circuits, during phonograph operation, thereby to increase the amount of energy available to said oscillator tube from said supply source when said tube is utilized to excite said lamp.

9. In a radio-phonograph combination, a radio receiver circuit of the superheterodyne type including vacuum tube amplifiers and a high frequency vacuum tube oscillator circuit, a source of limited energy supply for said vacuum tube oscillator and for the vacuum tube amplifiers in said receiver circuit, a photoelectric phonograph pickup device including a light source consisting of an electric lamp, means for selectively affecting radio or phonograph operation, means for supplying energy from said oscillator circuit to said lamp during phonograph operation, and means operative during phonograph operation to reduce the number of individual vacuum tube loads on said energy supply source and for incr'easingthe voltage on'sai'd oscillator tube,

Vthereby to increase the high'frequency power availableffor the excitation of said*Ianniy Y 10. In a combined carrier WaVeLreeiVer-phonograph combination, carrier Wavereceiving'apparatus'including high frequency current generating means forming an Voperative part ofjsaid apparatus, an Yeleotro-optical phonograph pickup device including anelectric lamp, means for selectively effectingV carrierwiraA/eVV reception or phonograph operation, and means for supplying high frequency current' from said generating means to said Alamp during phonograph operation.

11. In a radio-phonograph combination, a

MILTON L. THOMPSON.

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