US2476174A - Amplifier power supply - Google Patents

Description

July 12, 1949.

Carrier Wave Amplifier and Tuner R. ADLER ETAL AMPLIFIER POWER SUPPLY Filed NOV, 10, 1945 Fig./

ROBERT AOLER HENRY P. KALMUS INVENTORS.

Y M mm h-l I- V I THEI'R Arron/vars Patented July 12, 1949 AMPLIFIER POWER SUPPLY Robert Adler and Henry P. Kalmus, Chicago, Ill.,

assignors to Zenith Radio Corporation, a corporation of Illinois Application November 10, 1945, Serial No. 627,930

3 Claims.

This invention relates to amplifiers and more particularly to arrangements for supplying electron discharge amplifying devices with operating current from a main power supply.

For a long time it has been common to rectify alternating current from a mains power supply and to filter carefully the resulting pulsating rectified current to provide smooth continuous current for the operation of electron discharge amplifier devices, particularly in radio receivers.

Many attempts have been made with varying degrees of success to cheapen the filters required for smoothing such rectified pulsating current. It has been proposed to utilize unfiltered pulsating rectified current in balanced amplifiers, but such arrangements have never been successful because of the extreme difliculty in making balanced amplifiers precisely linear, with consequent cross-modulation in those amplifiers between the pulsating components of the discharge currents applied thereto and the signal.

Another known arrangement for utilizing unsmooth pulsating rectified current is described in Patent 1,720,914-Miessner. In this arrangement, a single electron discharge device produces the final power amplification of the signal and the output of that amplifier is connected to an output transformer, the primary of which has a center tap which is connected to a source of unsmoothed pulsating rectified current. That is, one terminal of the primary of this output transformer is connected to the anode of the single final amplifier tube, and the other terminal of the center tapped primary is connected to the anode of a preceding amplifier tube or tubes, whose anode resistance is substantially equal to the anode resistance of the final amplifier tube. By that arrangement, a bridge circuit is formed of which the four arms are respectively the two halves of the primary of the output transformer, the discharge path of the final amplifier tube, and the discharge path of the preceding tube or tubes.

It is an object of the present invention to provide such an arrangement with greater power output and less loss of signal power in the output transformer.

It is a specific object of the present invention to provide an improved arrangement in which an output transformer in a signal amplifier system, together with the electron discharge amplifier devices is used as a part of the filter arrangement to prevent the alternating current component of a pulsating supply voltage from appearing at the output terminals of the system,

2 and in which a minimum of signal power is dissipated in the filter.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with accompanying drawings in which:

Figure 1 illustrates a preferred embodiment of our invention; and

Figure 2 illustrates an alternative arrangement thereof.

In Figure 1 a radio receiver, having its input terminals connected to an antenna l and ground 2, includes a carrier wave amplifier and tuner 3 which may be of any conventional form and which includes electron discharge amplifier devices for which smooth continuous current is required. The receiver also includes a carrier wave detector, and signal amplifier device 4, a signal power amplifier device 5, an output transformer 6, and a speaker l.

A carrier wave detector and amplifier device 4 is connected to the high frequency output terminals of the carrier wave amplifier and tuner 3 through conventional circuits and the anode 8 of the device 4 is coupled through a condenser 9 to the control electrode IU of the device 5 so that amplified signals appearing on anode 8 are impressed on the control electrode Hi. The cathode ll of the device 5 is connected through a biasing resistance l2 to ground, and the control electrode ll] of device 5 is connected through a suitable grid resistance I3 to ground. The anode 14 of device 5 is connected to one terminal of the primary l5 of output transformer 5. The secondary winding l6 of transformer 6 is connected to a speaker I through which signals are reproduced.

For the supply of operating current to the discharge devices 4 and 5 and to the discharge devices in the carrier wave amplifier 3, a two terminal plug I1 is arranged to be connected to a main power supply, one of the plug terminals being grounded (for example, to a ground bus insulated from the chassis) and the other being connected to the anode l8 of a power rectifier device IS. The cathode 20 of the rectifier I9 is connected through a surge current protecting resistance 2| to a tap 22 on the primary l5 of transformer 6, and the tap 22 is connected through a by-passing condenser 23 to ground.

A small amount of smoothing of the current rectified by the device I9 is produced at the condenser 23 by reason of the fact that the device l9 recharges the condenser 23 before it becomes substantially discharged through the load circuit. Nevertheless, some alternating voltage appears across condenser 23 and is therefore impressed between tap 22 and ground (or the ground bus, where one is used).

The lower terminal of the primary of transformer 6 is connected serially through a resistance 24 and a large by-pass condenser 25 to ground. The screen electrode 26 of device 5 is connected through a large by-pass condenser 21 to ground and is also connected through a resistance 28 to a point between resistance 24 and condenser 25. The anodeB of device 4 is connected through a resistance 29 to the screen electrode 26 of device 5 and the anodes and screen electrodes, if any, of the amplifier devices in the carrier wave amplifier 3 may similarly be connected to the screen electrode 26 of device 5.

Discharge current is therefore supplied through the rectifier l9 as follows: Current flows from cathode 2!] through resistance 2|, to the upper half of primary |5 of transformer H6, anode l4, cathode H, and resistance |2 to ground. Discharge current also fiows from cathode 2!] through resistance 2|, the lower part of primary l5 of transformer 6, resistance 26, resistance 28, screen electrode 26, cathode H, and resistance l2 to ground. It also flows from cathode through resistance 2| and the lower part of primary |5, of transformer 6, resistance 24, resistance 28, resistance 29, anode 8, and the cathode of device 4 to ground. The passage of discharge current for the screen electrode 26 and for the anode 8, as well as for the amplifiers in the amplifier 3, through resistances 24 and 28 smooth that current by reason of the filtering action of condensers and 2'! so that such current is substantially free of any alternating component. That is, substantially no alternating voltage exists across condenser 21.

Alternating voltage impressed between tap 22 and ground produces a flow of alternating curwent through the anode M of device 5, but the circuit is arranged in a bridge fashion described hereafter so that this alternating current, so long as device 5 operates with substantial linearity, has substantially no effect in the secondary l6 of transformer 6. For this purpose, the two parts of the primary l5 of transformer 6 are arranged to form a bridge with the device 5, resistance 24 and condenser 25. That is, in its average operating condition, a predetermined resistance exists between anode M of device 5 and ground through the discharge path of that tube 5, and the ratio of that resistance to resistance 24 is made equal to the ratio of the number of turns between tap 22 and the upper terminal of primary |5 to the number of turns between tap 22 and the lower terminal of primary I5 of transformer 6. Condenser 25 is very large and olfers little impedance to the flow of alternating current at the frequency of the alternating voltage impressed on tap 22. With such a bridge arrangement, alternating voltage on tap 22 causes alternating current flow through the upper part of primary l5 in such amount as exactly to cancel the flux threading secondary l5 caused by the flow of alternating current through the lower part of primary 5 caused by alternating voltage on tap 22. Therefore, even though alternating current flows through the space charge path of device 5, and

through the upper part of the primary l5 of transformer 6, no corresponding sound is caus d in speaker I because the consequent flux in transformer 5 is cancelled out by an opposite flux produced by alternating current flow through the lower part of primary l5, and the alternating voltage on tap 22 has no effect unless device 5 is caused to operate in a non-linear region so that the signal which it amplifies is modulated b the alternating voltage on tap 22.

Since device 5 is usually a power amplifier, and requires a large amount of space current in proportion to the amount of space current required by preceding amplifiers such as device 4, or even b the screen electrode 26, the tap 22 might be placed relatively near that terminal of primary Hi which is connected to anode M and resistance 24 made large. Such a course, however, would not only provide relatively low voltage to the screen electrode 25 and to the anodes of the preceding discharge devices, with a consequent reduction in the sensitivity of the receiver, but also would cause the loss of signal power in that part of primary I5 below tap 22. It has been found that such effects are avoided by placing tap 22 quite near the lower terminal of primary l5 of transformer 6 and by making resistance 22 relatively small, so that large discharge currents at relatively higher voltage may be supplied to screen electrode 25 and to the anodes of the preceding electron discharge devices, and also so that a minimum amount of signal power is dissipated in resistance 24. It is preferred to make the impedance of primary l5 sufficiently low with respect to the impedance required for maximum power to avoid modulation of the signal by alternating voltage on tap 22.

It is possible, when it is anticipated that the internal resistance of tube 5 will increase With age to place tap 22 somewhat nearer to the lower terminal of primary I5 than would be dictated by a precise balance of the bridge, so that, as the internal resistance increases, the bridge will become more nearl balanced.

It should be understood that it is within the broad scope of the invention to use a triode in place of pentode amplifier 5 or alternatively to connect screen electrode 25 to tap 22 so that it is supplied with relatively unsmoothed voltage. Both of these arrangements are susceptible of adjustment as described above to balance out the hum, but they are not preferred because the balancing required is much more critical and difiicult than with the arrangements shown in Figure l. The greater difficulty in balancing such alternative arrangements arises because greater alternating currents flow in the arms of the bridge, and, since there exists a fairly definite maximum tolerable amount of alternating voltage in secondary |6, larger alternating currents in the primary make it more dificult to obtain the precision of balance required to produce only the maximum tolerable alternating voltage in secondar It.

In Figure 2 many elements are identical with those illustrated in Figure 1, and like reference characters are applied to them. In this arrangement, the resistance 24 instead of being connected to the lower terminal of primary l5 and transformer 6, is connected to tap 22 and provides merely the usual form of filtering action for discharge current fiowlng to screen electrode 26 and to the anodes of the preceding discharge device. The lower terminal of primary I5 is connected through a resistance 30 to movable member 3| of a switch, which has two fixed contacts 32 and 33. Contact 32 is grounded and contact 33 is connected through a large condenser 34 to ground. With member 3| connected to contact 32, the resistance 30 allows the flow of rectified current from the cathode 20 of device [9 through the protective resistance 2!, the lower part of primary l and resistance 30 to ground. If the flow of such current may be tolerated, the ratio of resistance 30 to the anode to ground resistance of device 5 is made equal to the ratio of the num-- ber of turns in primary l5 between tap 22 and resistance 30 to the number of turns between tap 22 and anode 14. Under such conditions a bridge circuit is formed in which the flow of alternating currents from tap 22 upward through primary I5 creates a flux in transformer B which is exactly counterbalanced by flux produced by the flow of alternating current from the tap 22 downwards through the lower part of primary 15. Similarly, in this bridge arrangement, it is preferred to place tap 22 relatively near the lower terminal of primary IS in order to avoid the dissipation of any substantial signal power in resistance 30.

With switch member 3| in connection with contact 33, condenser 34 being sufficiently large as to offer no substantial impedance to the flow of current at the frequency of the alternating voltage on tap 22, the same result is achieved and the bridge is balanced, but no rectified current flows through resistance 30, and the rectifier I9 may, therefore, be made smaller at the cost of adding condenser 34.

It should be understood that it is within the scope of this invention to utilize this arrangement in any signal amplifier which can be operated substantially linearly and whose output may be connected to a load through a transformer in which fiux may be induced to cancel flux produced by the undesired currents. For example, the part of primary I5 below tap 22 may be an entirely separate winding, or under certain conditions, secondary l6 may be used to create the cancelling flux.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

We claim:

1. In combination, a source of pulsating voltage and a bridge circuit, said bridge circuit including an electron discharge amplifier device having an anode and a cathode, an output transformer having a primary winding, one end of said winding being connected to said anode, a load resistor having one terminal thereof connected to the remaining end of said primary winding and having the other end effectively connected to said cathode, a tap connection on said primary winding displaced from the center of said primary toward said remaining end to form a large and a small portion, said source of pulsating voltage having a, first and a second terminal, said first terminal being connected to said tap connection, said second terminal being eifectively connected to said cathode, the ratio of the number of turns in said large portion being substantially equal to the ratio of the magnitude of the anode to cathode resistance of said amplifier device to the magnitude of the resistance of said load resistor, whereby said bridge circuit is balanced, said pulsating currents produce no ill effects in the output from said electron discharge amplifier device, and the loss of audio power in said load resistor is minimized.

2. In combination, a source of pulsating voltage and a bridge circuit, said bridge circuit including an electron discharge amplifier device having an anode and a cathode, an output transformer having a primary Winding, one end of said winding being connected to said anode, a load resistor having one terminal thereof connected to the remaining end of said primary winding and having the other end connected to a filter network including a filter condenser, said filter network having a functional terminal and a grounded terminal, said load resistor cooperating with said filter condenser to perform a filtering action on pulsating currents flowing therethrough to said functional terminal of said filter network, and a utilizing network connected between said functional terminal and said grounded terminal of said filter network.

3. A bridge circuit including an electron discharge amplifier device having an anode and a cathode, an output transformer having a primary winding, one end of said winding being connected to said anode, a load resistor having one terminal thereof connected to the remaining end of said primary winding and having the other end effectively connected to said cathode, a tap connection on said primary winding displaced from the center of said primary toward said remaining end to form a large and a small portion, the ratio of the number of turns in said small portion being substantially equal to the ratio of the magnitude of resistance of said amplifier device to the magnitude of resistance of said load resistance, whereby said bridge is balanced and the loss of useful output from said electron discharge amplifier device is minimized.

ROBERT ADLER. HENRY P. KALMUS.

REFERENCES CITED UNITED STATES PATENTS Name Date Miessner July 16, 1929 Number

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