US2002343A - Power circuits - Google Patents

Description

May 21, 1935. ENGEL 2,002,343

POWER CIRCUITS Filed April 12, 1933 /NPU 7' VOL 75 LOUD Z SPEAKER FIELD INVENTOR FRANCIS H. E/VGEL ATTORNEY Patented May 21, 1935 UNITED STATES PATENT OFFICE POWER CIRCUITS Francis H. Engel, New

York, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application April 12, 1933, Serial No. 665,641

3 Claims.

The present invention relates broadly to power supply circuits for amplifiers utilized in communication systems and the like. More particularly, the present invention is primarily directed to a 5 novel rectifier and filter circuit arrangement for radio receivers.

An object of the invention is to provide a circuit arrangement for amplifiers utilizing thermionic tubes and employing a loudspeaker with a field winding energized by the rectified current. A still further object of the invention is to provide a single rectifier tube employing preferably two anodes and two indirectly heated cathodes connected so that the rectified current for the loudspeaker field winding is obtained from one half of the tube while the rectified current for energizing the electronic tubes of the rectifier is obtained from the other half of the tube.

Further objects of the invention will be apparent from a reading of the following specification and accompanying drawing.

In the drawing, Fig. 1 illustrates diagrammatically a preferred embodiment of the invention. utilizing a rectifier tube as above described for separately deriving two rectified currents; and,

Fig. 2 illustrates a circuit utilizing the invention in connection with so-called transformerless receivers.

Small receivers and particularly universal A. C.D. C. sets, due to the fact that no power transformers are utilized, are limited in their performance capabilities to a great extent by the low plate supply voltages available. For example, it has been found that an increase of only a few volts in the applied plate voltage will appreciably raise the power output of an electronic tube such for instance as the type 43 tube with a corresponding increase in tone quality. Consequently, a satisfactory means of increasing the available plate supply voltage can be translated into improved performance. In receivers utilizing a small number of tubes it is possible that the plate current drain is less than the speaker field current and the present invention ofiers a means for increasing the available D. C. voltage other than by the use of transformers in such small receivers employing a dynamic speaker by the utilization of each plate of a rectifier tube employing two anodes and two cathodes to supply each load circuit separately.

A tube suitable for this purpose is known in the art as type 25Z5 and such a tube has been shown in the drawing. This tube is a high vacuum rectifier of the heater cathode type and comprises two anodes and two indirectly heated cathodes. Each half of the tube can be operated independently of the other provided good regulation of the supply voltage is obtainable.

Tests have indicated that the rating of this socalled 25Z5 tube is ma, and that each half of the tube can handle 50 ma. According to the present invention the tube is used to energize a dynamic speaker field from one plate and cathode of such a tube and to supply plate voltage to the tubes in the receiver from the other half thereof. It has been found that the current drain on each half with such an arrangement will not exceed the allowable 50 ma. in most small receiver designs. In addition, it has been found that a reduction in ripple voltage can be obtained with the same total filter condenser capacity as when used with the two halves supplying a single circuit. In tests conducted to determine the increase in D. C. voltage available for the plate supply with an arrangement as disclosed herein over the voltage available when the plates of the tube are operated in parallel, it has been found that as regards the operating characteristics of the 25Z5 tube with the plates and cathodes paralleled, and with each plate and cathode operated individually, a material increase in voltage available is obtained with the two halves of the rectifier operated individually. In particular, tests have been run utilizing the circuit in connection with a five tube superheterodyne receiver employing 2-36 type tubes, 139 type tube, 143 type tube and l25Z5 rectifier. The plate and screen current drain for these tubes was found to be approximately 32 ma. The speaker field was found to draw approximately 45 ma. With the plates of the 25Z5 rectifier tube operated in parallel the total current to be supplied will, of course, be 75 ma. With the plates operated separately one plate must supply 32 ma. for the plates of the tubes and the other 45 ma. for the speaker field.

In the above example, assume for instance that with the plates operated in parallel a 16 mi. condenser is used in the filter, and with the separate operation of the two halves two 8 mi. condensers one for each plate are used. It was found that the voltage input to the filter was 102 volts in the case of plates operated in parallel and volts in the case of the plates operated individually. This represents a gain of 8 volts in available plate supply voltage which, as previously pointed out, is of utmost importance. While this increase in available plate voltage gives noticeable improvement in the operation of the 36 type tubes and the 39 type tube of the receiver tested the 43 type tube derived the greatest benefit inthrough a coil ll, while cathode I asmuch as an 8 volt increase on the plate was found to raise the power output approximately 20 percent. Increased output from small receivore is extremely desirable in that more pleasing tone quality usually accompanies the higher output. 7

In Fig. l, 3 represents a power transformer having a primary winding to which analternating current power supply is applied to the terminals l and 2. The secondary of the transformer 23 is adapted to impress the necessary voltage across the rectifier tube M3 as will be hereinafter described. As is obvious from the drawing tube to is constructed with two anodes! and 5, to indirectly heated cathodes E and I and the series heater circuit for both cathodes identified in the drawing by the numeral 8. The two anodes d and 5 of the rectifier tube iii are connected to one end of the secondary of transformer 3, while cathodes 6 and I are connected to the other end of the secondary of transformer 3, cathode 6 is connected to this same end of the secondary of transformer 3 through a choke coil 12 and a load circuit (not shown) connected across the terminals l6 and ii. The choke coil l i may be the field coil or" a loudspeaker or other reproducer associated witl the receiver. 'By-pass'condenser i3 is provided effectively shunted across the coil ll while the usual filter condensers i l and is are provided for by-passing alternating current components or" the rectified current and thus prevent these alterhating current components from being impressed upon the load circuit connected to terminals l6 and ill. It is to be understood that the heater circuit 3 may be suitably energized by a suitable transformer connected to the same source as is the transformer 3. I

In Fig. 2, the same type oicircuit is shown as is shown in Fig. 1 except that no power trans formers are shown, intact, the rectifier is connected to the usual house power network directly at terminals 5 and 2. The heater circuit is connected to the network at terminals i5 and it! through suitable voltage reducing means if such are required.

lhe circuit arrangements disclosed necessitate the use of an additional filter condenser or a two section unit condenser. However, the advantages which can' be derived from the increased voltage available for plate supply more than onset the slight cost of the additional filter condenser or the two section unit condenser.

The effector any hum introduced the speaker by the ripple present in the field supply voltage due to incomplete filtration ofthe rectified current may be reduced to a very low level by the use of a loudspeaker which operates on a current having a slight ripple. The extra cost of this type of loudspeaker is slight whereas it would be necessary to have a condenser having a capacity of at least 24 mi. to reduce the hum level to a satisfactory value. The cost of such a con denser is quite high considerably higher than the extra cost of a loudspeaker arranged to operate with current having a slight ripple. It has been found that by using this type loudspeaker the hum will be reduced to a level comparable to that obtained by using a 32 mi. condenser in the filter.

It will be understood that the principles of this invention may be embodied in various forms and that the present embodiments of the invention are to be considered as indicative.

. 1. In a power supply circuit for energizing amplifying apparatus from either alternating current or direct current power mains, said amplifying apparatus including at least one space dischargefdevice having an anode circuit and a reproducer provided with a field winding, an electronic tube having two anodes and two indirectly heated cathodes, a heating circuit for said cathodes; a connection from one terminal of the power mains to both said anodes, a connection from the other ternunal of the rectifier cathodes, said last named connection including said field-winding, a filter condenser shunted across said field windingfa connection from the other cathode to the last named terminal of the power mains including the anode circuit of the space discharge device and a filter condenser shunted across said anode circuit.

In a pot-versupply circuit for radio receiving apparatus provided with an output stage and a loudspeaker oi the electrodynarnic type coupled thereto, a house current supply source, a rectifier '16 mains to one of tube having a pair or" anodes and of indirectly heated cathodes, a connection from one terminal of the current supply source to both rectifier anodes, a connec ion from the other terminal cisaid source-to one of the rectifier cathodes, said last named connection including a choke coil adapted-to supply a magnetic field for the loudspeaker; and a connection from the other rectifier cathode to the output stage of the receiver including a choke coil for smoothing out the current supplied to said stage.

3. In a power supply circuit for amplifying apparatus adapted to be connected to direct current and alternating current sou cos of p wer supply, said amplifying apparatus being provided with at least one space discharge device requiring unidirectionalancde circuit energizing current a reproducer or" the type having a field winding arranged so as to be energized by uni-directional current, an electronic rectifier tube having two anodes and tw indirectly heated cathodes, a heating circuit for said cathodes, necting both said anodes to a terminal of the available power supply, means to connecting one of said cathodes to another terminal of the pcwer supply, said last named means including the field winding of the reprjoducer and current smoothing means, and means for connecting said last named terminal or" the source or" power supply to the other of said cathodes said last means including the anode circuit of the space discharge device and current smoothing means.

FRANCIS H. ENGEL.

means for con-'

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