US2789235A - Voltage dropping system for phonographs with amplifiers - Google Patents

Description

April 1957 J. R. SHOAF u 2,789,235

VOLTAGE DROPPING SYSTEM FOR PHONOGRAPHS WITH AMPLIFIERS Filed Nov. 18, 1954 IN V EN TOR.

2,789,235 VOLTAGE DROPPING SYSTEM FOR PHONO- GRAPHS WITH AMPLIFIERS James R. Shoat H, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November 18, 1954, Serial No. 469,603 7 Claims. (Cl. 307-112) The present invention relates to electric phonographs and more particularly to power supply circuits for use with phonographs of the type which include audio frequency sound amplifiers and which are designed for operation from one or more different power line voltages.

In general, and as used herein, an electric phonograph includes a mechanical record playing apparatus driven by an electric motor and a self-contained audio frequency amplifier. In many instances it is desirable that the phonograph be operable from one or more power line voltages, the most commonly available voltages being 110 volts A. C. and 220 volts A. C. The previous practice in 110/220 volt phonographs was to provide a twowinding motor with the windings connected in parallel for use with l10-volt power lines in series for 220-volt power lines. The amplifiers were designed for 110-volt operation and one or more high wattage resistors were used to drop the 22% volts to 110 volts with the accompanying power loss and heat problem in compact instruments. It is possible to use transformers to change the power line voltages, but the addition of a transformer to the phonograph not only increases the cost of the equipment but adds to the size and weight with no appreciable advantage in use.

It is an object of this invention to provide a simplified power supply circuit for electric phonographs which is readily operable from one or more power line voltages, with a high degree of eificiency.

It is another object of this invention to provide an improved phonograph system operative on one or more power line voltages which utilizes only components already a part of an electrical phonograph designed for operation from a single power line voltage.

It is a further object of this invention to provide an improved electric phonograph system which is operable from one or more power line voltages with no unnecessary power loss and accompanying heat dissipation resulting therefrom.

it is still a further object of this invention to provide a simplified power supply circuit for electric phonographs which may be manufactured in large quantities at low cost and which has no unnecessary heat dissipation thereby permitting a more compact construction.

In accordance with the invention, the phonograph is provided with a motor having a pair of field windings which may be connected in parallel for operation at a low voltage such as 110 volts, and in series for operation at a higher voltage such as 220 volts. The audio frequency amplifier which is self-contained in the phonograph, and designed to operate from a single voltage, is connected across one of the field windings. It is, of course, understood that the audio frequency amplifier may be a portion of a signal receiver or the like in a radio-phonograph instrument. In effect the motor windings are used as an auto-transformer to supply the same operating voltage to the audio frequency amplifier, which is provided with a fixed connection therewith, while only the motor windings are switched to conform to the supply line voltage.

The novel features that are considered characteristic of this invention are set forth with particularity in the pending claims. The invention itself, however, both to its organization and method of operation, as well as adited States Patent 'ice ditional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing.

Referring to the sole figure, a single stage audio frequency amplifier having an amplifier tube 5, is connected between an electric phonograph pickup device 6 and a sound reproducer or loud speaker 7 in a conventional phonograph amplifier circuit. Volume control means for the phonograph amplifier is indicated at 8 and includes a variable volume control connection 9 for the amplifier tube 5 and an input voltage dropping resistor 19 between the pickup device and the volume control element 8.

The tube 5 may be of the filamentary type or of the cathode heater type shown in the present example, in which the cathode 11 is provided with a suitable heater element 12.

The anode circuit of the amplifier 5 is connetced to one end of a primary winding 13 of an output transformer to a source of operating potential +B which is connected to the tap 14 on the transformer. The screen electrode of the amplifier 5 is connected to the other end of the primary winding 13 and to the source of operating potential +B at the transformer tap 14.

The rectifier for supplying anode and other operating potentials to the amplifier is indicated at 16 and comprises an anode 17 which is connected through a lead 18 to one side of the power supply line 19. The rectifier 16 also has a cathode 20 which is connected with the positive anode supply lead 21 of the phonograph amplifier, through a filter comprising a series resistor 22 and the usual shunt filter capacitor 23. The opposite side of the power supply line 24 is connected through an operating switch 25 to a supply lead 26 which, in turn, is connected to system ground 27 thereby forming a return circuit for the anode and other operating supply circuits. The system ground 27 is provided by a common wiring which is isolated from the chassis and is connected through the capacitor 28 to the conductive chassis 29 on which the amplifier and record changer mechanism are mounted.

The rectifier is provided with a heater element 30 for the cathode 20 which is connected in series with the cathode heater 12 for the amplifier tube 5 through a series resistor 32. This series circuit is connected to the lead 18 which forms one side of the power supply line and is connected through ground to the lead 26.

The electric motor for the electric phonograph turntable 35 has a pair of substantially similar field or operating windings 36 and 37 which are connected to a manually operable double-pole, double-throw switch 38 which provides a convenient means for alternatively connecting the field windings in series or in parallel. The double-pole, double-throw switch has a plurality of contact terminals 39, 40, 41, 42, 43 and 44 to which the field windings and power supply are connected. The winding 36 is connected to a pair of terminals 39 and 44 respectively while the winding 37 is connected to a pair of terminals 40 and 41. The or 220 volt power line (not shown) is connected through a plug 45 and the supply lines 24 and 19 to the terminals 39 and 41 of the switch 38, and a jumper is connected between the terminals 40 and 43.

For 220 volt operation the double-pole, double-throw switch is in the portion shown in solid line, wherein the terminal 44 is connected with the terminal 40 while the terminal 39 is connected with the terminal 42. The field windings 36 and 37 are thus connected in series. Tracing the circuit from the supply line 19 which is connected with the terminal 41, the winding 37 is connected from the terminal 41 to one side of the winding 36 through the terminals 49 and 44. The other side of the winding 36 is connected through the terminal 39 to the supply line 24. e In the 220 volt position of the switch 38, the audio frequency amplifier is connected with the terminals 40 and 41 or directly in parallel with the field winding 37. Since the total power line voltage is developed across the series combination of the windings 36 and 37, the voltage across either is substantially on half of the line voltage. Thus 110 volts is'supplied to the audio frequency amplifier. The field windings in effect act as a step-down auto-transformer in which the serially connected windings 36 and 37 are connected across the 220 volt power line and the audio frequency amplifier power supply is connected across the winding 37.

For llo-volt operation the double-pole, double-throw switch 38 is moved to the position shown in the dotted lines, and the connections are broken between the terminals 42 and 39 and 40 and 44 respectively. The field windings are thus connected in parallel. Tracing the circuit, the field winding 37 is connected to the supply lead 19 at the'terminal 41 and to the supply lead 24 through the terminals 43 and 39. The winding 36 is connected to the power supply lead 24 at the terminal 39 and is connected by way of the terminals 44 and 41 to the supply lead 19.

In the 110-volt position of the switch 30 the audio frequency amplifier is connected with the terminals 49 and 41 or in parallel with both the field windings 36 and 37. Since the phonograph audio frequency amplifier was designed to operate on 110 volts A. C., the 110 volt line voltage which is across the parallel-connected windings 36 and 37 'is available to the amplifier. In other words the phonograph amplifier is directly across the llO-volt .power line through the lead 18 which is directly connected to the power supply lead 19, and the lead 26 which is connected through the terminals 40, 43 and 39 to the lead 24.

Thus, by simply connecting the phonograph record .player motor field windings in parallel or in series, the phonograph is conditioned for operation from either 110 or 220 volts'A. C. power source, the self-contained amplifier or the line being'at all times connected in parallel with one of the field windings,'and in either case being energized by 110 volts A.'C. It should be understood that the invention is not restricted to the particular voltages'men- 'tioned, but 'is-applicable to other A. C. voltages.

An electric phonograph system constructed in accordance with the invention does not require any special. components such as a motor with special field windings or voltage dropping resistors or the like. The motor used with the phonograph of the invention can be manufacturedfor substantially the same cost as the motors ordinarily used with phonographs for operation from a single ,power line voltage,- and in many cases the last mentioned motors 'are'actually provided with two field windings. It should be notedas a feature of the invention that both field windings are used for operation on 110 volts and .220 volts. The elimination of the voltage dropping resistors which necessarily must be of high wattage rating considerably reduces the expense of the apparatus. In addition, the elimination of these resistors does away with unnecessary power loss, and the accompanying heat dissipation thereby enabling the construction of a more com- :pact phonograph apparatus without causing overheating of'other components. The only additional components required -by the present system, not required in a phonoigraph system for operation for a single power line voltage,

-is the provision of monster changing the connection of the field windings from series to parallel.

It can be seen that in accordance with the invention,

this new and improved electric phonograph circuit efleo' :tively provides for operation on two or more ditferent 'lin e voltages and utilizes the operating or field windings lot the driving motor as an auto-transformer for deriving the proper power line voltage for the self-contained audio frequency amplifier. This system, as has been shown, may utilize components already a part of an electrical phonograph designed for operation from a single power line voltage and does not have the disadvantage of unnecessary power loss and the problem of heat dissipation.

What is claimed is:

1. An electric phonograph system for operation at one or more diiferent alternating current power line voltages comprising in combination, an audio frequency amplifier adapted to be energized at a predetermined alternating current voltage, a phonograph motor having a pair of operating windings, means for connecting said operating winding to operate in parallel for a first power line voltage and in series for a second high power line voltage, and means providing a fixed connection for said amplifier in parallel with one of said operating windings.

2. An electric phonograph system for operation at a first and a second alternating current power line voltages comprising in combination, an audio frequency amplifier adapted to be energized at said first alternating current power line voltage, a phonograph motor having a pair of operating windings, means for connecting said operating windings in parallel for operation of said first power line voltage, means for connecting said operating windings in series for operation on said second power line voltage, and means providing a fixed connection for said amplifier in parallel with one of said operating windings.

3. An electric phonograph system for operation at a first and a second alternating current power line voltages comprising in combination, an audio frequency amplifier adapted to be energized at said first alternating current power line voltage, a phonograph motor having a pair of operating windings, manual switching means for alternatively connecting said operating windings in parallel for operation of said phonograph at said first power line voltage or in series for operation at said second power line voltage, and means fixedly connecting said amplifier in parallel with one of said operating windings.

4. -An electric phonograph system as defined in claim 3, wherein said manual switching means comprises a doublepole, double-throw switch.

5. A power supply circuit for use with phone-graphs of the type which include an audio frequency signal ampli fier and which are adapted to operate with one or more different alternating current power supply voltages comprising, a phonograph motor having a pair of field windings, connection means for connecting said field windings with an alternating current power supply circuit, manual switching means for alternatively connecting said field windings in parallel for operation of said phonograph at a first power supply voltage or in series for operation at a second power supply voltage, and means fixedly connecting said amplifier in parallel with one of said operating windings.

6. A power supply circuit for use with phonographs of the type which include an audio frequency signal arnplifier and which are adapted to operate on power line voltages of either or 220 volts A. C., comprising a phonograph motor having a pair of like field windings, connection means for connecting said field windings with an alternating current power line, manual switching means for alternatively connecting said field windings in parallel for operation of said phonograph at the power line voltage of 110 volts A. C. or in series for operation at the powerline voltage of,220 volts A. C., and means fixedly-connecting said amplifier in parallel with one of said operating windings.

7. A power supply circuit for use with pho-nographs .as defined in claim 6 wherein said manual switching means comprises a'double-pole, double-throw switch.

Kneisley May 9, 1939 Anderson et a1. -J an. 18, 1949

Images