US2252057A - Heater circuit for radio apparatus - Google Patents

Description

Aug. 12, 1941. e. w. BLESSING HEATER CIRCUIT FOR RADIO APPARATUS Filed May 31, 1939 Zimoentor Patented Aug. 12, 1941 UNITED STATEd TENT OFFICE Gregory W. Blessing, Moorestown, N. J assignor to Radio Corporation of America, a corporation of Delaware Application May 31, 1939, Serial No. 276,673

9 Glaims.

The present invention relates to heater circuits for radio apparatus, and more particularly it relates to a circuit of the series type in which the cathode heating current for a plurality of tubes traverses the various heaters or filaments successively, and is controlled by a ballast or series resistor for reducing the higher voltage of the supply circuit to the proper value for the series heater circuit. As is Well known, the series ballast resistor for a cathode heater circuit introduces an appreciable loss which is dissipated in the form of waste heat. It is therefore an object of the present invention to provide an improved cathode heater circuit wherein the energy loss of the usual ballast resistor is eliminated and wherein said energy is converted into useful work.

In any radio apparatus, such as a radio receiver, phonograph or amplifier, some portion of the power supply circuit includes apparatus having an inductive winding or other voltage drop producing device from which energy is taken to operate the apparatus or some portion thereof. For example, such potential drop producing device may be a transformer winding for the power supply circuit or a motor winding for the operation of a phonograph element of the apparatus. In either case, the potential drop producing device is designed to function under predetermined current and voltage conditions. In accordance with the invention, the potential drop producing device, such as the motor or transformer winding referred to, is designed to have a proper voltage drop or a current satisfactory to operate the apparatus with the energy that would otherwise be dissipated in the form of heat. To do this, the design of the winding or potential drop producing device is altered to establish in the series cathode heating circuit the same voltage drop as the usual series ballast resistor.

A ballast resistor in the form of a ballast tube usually dissipates the waste heat in a confined space which requires special precautions in cabinet design and careful arrangement of parts to provide adequate ventilation. Other forms of cathode heating circuit ballast include the wellknown resistance power cord or external ballast resistor units connected between the sup-ply outlet and the apparatus consuming the energy.

In accordance with the invention, the cathode heating circuit or filament circuit of the series type is designed and the various cathode heaters or filaments are arranged therein, to provide a suitable operating current for the apparatus to be operated by the cathode heating or filament current, and the potential drop producing portion of said apparatus is designed to provide the proper voltage drop at that current to produce at the terminals of the cathode heating or filament circuit the proper potential therefor.

The invention will, however, be better understood irom the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Figure 1 is a schematic circuit diagram of an amplifier and associated loudspeaker, motor and pickup elements constituting an electric phonograph embodying the invention; and

Figure 2 is a further schematic circuit diagram of the cathode heating and power supply circuits of radio apparatus also embodying the invention and illustrating a modification of the circuit of Fig. 1.

Referring to Fig. l, a two-stage audio frequency amplifier comprising a first stage amplifier tube 5 and a second stage or output amplifier 6 is connected between an electric phonograph pickup device l and a sound reproducer or loudspeaker 8 in a conventional phonograph amplifier circuit. Volume control means for the phonograph pickup is indicated at 9 and includes a variable volume control connection it] for the first amplifier tube 5 and an input voltage re ducing network I I between the pickup device and the volume control element 9.

The tubes 5 and 6 may be of the filament type or of the cathode heater type shown in the present example, in which the cathodes I2 and I3 are provided with suitable heater elements l4 and 55, respectively.

The rectifier for supplying anode and other operating potentials to the amplifier is indicated at It and comprises a pair of anodes ll connected through a lead IS with one side of the supply line i?! and having a corresponding pair of cathodes 29 connected with the positive anode supply lead 2| of the receiver through a filter comprising a series choke coil 22 and the usual shunt filter capacitors 23. The opposite side of the power supply line 24 is connected through an operating switch 25 with a supply lead 26 connected to the chassis or ground of the amplifier as indicated at 21, thereby forming a return circuit for the anode and other operating supply circuits.

The rectifier is provided with heater elements 23 for the cathodes 20 which are connected through a lead 29 and a lead 30 in series with the cathode heaters l4 and I5 for the amplifier tubes in a series cathode heater circuit, the supply leads of which are indicated at 3| and 32.

One lead 31 of the cathode heater circuit is connected to the lead and through the switch 25 to one side of the power supply circuit 24. The ordinary method of power supply utilizes a resistor to dissipate the wattage required to reduce the line voltage down to that required by the filament or cathode heater circuit. In accordance with the invention, however, the inductive apparatus in the system is designed to operate at the current and the voltage drop required by the filament or cathode heater circuit and is placed in series with the potential drop producing element of the said apparatus.

In the present example, the electric motor for the phonograph turntable represented at provides a useful energy consuming device which may be placed in series with the cathode heater circuit to reduce the line voltage without the intermediary of ballast tube or resistor. This connection is made from the lead 32 through the motor operating windings 36 and 3'! to the opposite lead [9 of the power supply circuit. When the switch 25 is closed, the cathode heater or filament circuit and the motor are energized in a series circuit.

The motor windings 35 and 31 are designed to provide the necessary voltage drop at the current required to operate the heater circuit and serve to utilize the energy that would otherwise be dissipated in the form of heat. Furthermore, the circuit utilizes existing apparatus, whereby the method of providing filament energy without the use of a ballast tube is comparatively simpl and inexpensive. Heretofore, the ballast tube has represented an added expense to which must be added the cost of the socket for mounting the tube and the cost of providing the usual opening in the chassis for the socket.

As indicated hereinbefore, in providing the present circuit arrangement, the apparatus providing the potential drop is redesigned for lower voltage operation and, in the case of the motor, the air gaps are adjusted to different limits than in the case of a motor operating at normal supply voltages. Also, in the case of the usual motor, the coils 35 and 31 might be provided with 2600 turns of .008 diameter enamel covered wire, for example, while, in the present circuit, the motor coils ar wound with 1560 turns of .01 diameter enamel covered wire, thereby permitting the motor to operate at a lower voltage and with a higher current to provide the same wattage and power and with greater economy of operation. The motor coils are less expensive to manufacture and provide less 1 R losses. The first stage amplifier filament or heater I4 is preferably connected to the lower potential or ground side of the supply line, as shown, while the rectifier filament or heater 28 is connected next to the windings 36-31, more adjacent to the high side of the supply line.

If the apparatus does not include a motor, that is, if the radio apparatus is not a phonograph combination or a phonograph amplifier and motor combination, but includes a power transformer, it has been found that the primary winding of such a transformer may be utilized as a potential drop producing element for a cathode heater circuit, since the transformer may be designed to operate with lower voltage on the primary by changing the stepup turns ratio.

Referring to Fig. 2, a circuit arrangement of the character referred to is shown and comprises a power supply transformer 40, the high voltage secondary M of which is provided with the usual center tap A2 and terminal connections to the anodes 43 of a full wave rectifier tube 44. The cathodes 45 are connected with the positive output supply lead 46 and with the usual potential supply resistor or bleeder 41 through a suitable filter 48. In the receiver associated with the power supply circuit are provided a number of amplifier or other tubes 50, 5|, 52, the filaments or heaters 53 of which are connected in a series circuit 54 including the heaters 55 of the rectifier tube 44.

The primary 58 of the power transformer 40 is placed in series with the cathode circuit 54 and connected with the power supply leads 5"! and 58, the latter including a power switch 59. In this arrangement, the stepup ratio of the transformer 40 is higher than in the usual transformer so that the primary 56 may operate at a lower voltage than that supplied by the circuit 51-58. For example, it may operate at approximately volts, instead of the usual 120 volts, the remaining 40 volts being taken by the filament circuit 54. As indicated in Fig. 1, the heater or filament circuit may operate at 56.3 volts while the motor operates at 81 volts. This is because the supply voltage -120 volts is the vector sum of these voltages.

In case that the cathode heater or filament circuit does not require sufficient current to provide a desired energy input to a series connected power consuming device in the cathode circuit, additional elements may be connected therewith to increase the current. In the case of the transformer 45, the secondary load may be adjusted to secure any desired voltage drop for the filament circuit. It will be noted that this eliminates the usual secondary required for filament heating.

However, pilot lamps used in radio apparatus and the like may not be series connected with the cathode heater or filament circuit for the reason that in manufacture the resistance of such devices is not held to proper tolerances. Therefore, in the circuit of Fig. 1, for example, the pilot lamp for the apparatus, indicated at 60, is connected across a portion of th motor winding 31, where the change in resistance by so replacing the pilot lamp has no appreciable effect upon the operation of the circuit.

From the foregoing description, it will be seen that in radio, phonograph, and other electronic apparatus involving amplifier and other circuits, including a plurality of tubes, the filament or cathode heater circuit of such tubes may be of the series type and may include a motor or transformer winding as the series drop producing element of such circuit, thereby eliminating the cost of the usual ballast tube and circuit connections therefor, and eliminating the problem of dissipating heat in the cabinet design of the apparatus without additional expense and with improved operating efiiciency.

I claim as my invention:

1. In a multi-tube electronic apparatus, the combination with a power supply circuit for said apparatus, of an electric energy consuming device therein having a power input winding, a cathode heating circuit in which a plurality of said tubes are connected in series relation and with which said winding is series connected with said power supply circuit, said winding being operable at a vector potential less than the supply voltage by an amount equal to the potential drop in the cathode circuit, thereby to provide a power consuming ballast means for said cathode circuit.

2. In a multi-tube signal amplifying apparatus, the combination with a series connected cathode heating circuit, of a power supply circuit for said apparatus, and a power consuming device having a power input winding connected in series with said cathode heating circuit across said power supply circuit as a ballast device, said device being designed to operate at a vector potential less than the power supply potential by an, amount equal to the potential drop in said cathode heating circuit.

3. In a multi-tube electronic apparatus, the combination with a power supply circuit and a series cathode heating circuit, of series ballast means for said cathode heating circuit comprising a device having a normal power input winding serially connected with said cathode heating circuit and operative with the cathode heating current and at a voltage which adds Vectorially with the voltage of the cathode heating circuit to equal the voltage of the power supply circuit, and means providing a load on said device for producing a predetermined normal cathode heating current.

4. A phonograph system including, in combination, a plurality of amplifier tubes, means providing a series cathode heating circuit for said tubes, a phonograph motor having operating windings adapted to operate with the cathode heating current, means for supplying energy to said windings and to said cathode heating circuit in series, the operation potential for said motor across said windings being such that the vector sum of said potential and the potential across the cathode heating circuit is equal to the supply potential.

5. A phonograph system including in combination a plurality of amplifier tubes and a rectifier tube, means providing a series cathode heating circuit for said tubes, a phonograph motor having operating windings adapted to operate with the cathode heating current, means for supplying energy to said windings and to said cathode heating circuit in series, the operation potential for said motor across said windings being such that the vector sum of said potential and the potential across the cathode heating circuit is equal to the supply potential, said cathode heating circuit including a heater element for a rectifier tube connected therein adjacent to said motor windmgs.

6. A phonograph system including in combination a plurality of amplifier tubes and a rectifier tube, means providing a series cathode heating circuit for said tubes, a phonograph motor having operating windings adapted to operate with the cathode heating current, means for supplying energy to said windings and to said cathode heating circuit in series, the operation potential for said motor across said windings being such that the vector sum of said potential and the potential across the cathode heating circuit is equal to the supply potential, said cathode heating circuit including a heater element for a rectifier tube connected therein adjacent to said motor windings, and means providing a pilot lamp connection across a portion of one of said motor windings.

7. In a radio apparatus, the combination of a power supply circuit, a power transformer having a primary winding connected with said circuit, a rectifier tube and a plurality of amplifier tubes, a series cathode heating circuit for said tubes connected serially in circuit with said primary winding as a power input device for said transformer and as a ballast device for said cathode heating circuit, whereby a winding on said transformer for cathode heating and ballast resistor losses are eliminated.

8. In a radio apparatus, the combination as defined in claim 7, further characterized by the fact that a first amplifier tube is connected in said cathode heating circuit at the lower potential portion thereof with respect to ground and that the rectifier tube is connected in said circuit adjacent to the primary winding.

9. In a radio apparatus, the combination of a power supply circuit, a power consuming device having a winding connected with said circuit, a rectifier tube and a plurality of amplifier tubes, a series cathode heating circuit for said tubes connected serially in circuit with said winding whereby said winding serves as power input means for said device and as a series ballast means for said cathode heating circuit.

GREGORY W. BLESSING.

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