US1966221A - Amplifier - Google Patents

Description

Patented July It), 1934 AMPLIFIER Herre Rinia, Eindhoven, Netherlands, assignor to Radio Corporation of America, a corporation of Delaware Application November 17, 1931, Serial No. 575,561 In Germany May 28, 1931 6 Claims.

This invention relates to a circuit arrangement of thermionic tubes in which screen grids are provided, and may be used in radio receiving connections, amplifying connections and the like.

In said connections it is desirable that the average anode current of the tubes is kept constant, since variations therein always give rise to disturbances. Consequently, measures must be taken by which the production of variations in the anode current is counteracted. For this purpose a circuit arrangement as shown in the figures of the accompanying drawing may be used. In the drawing Fig. 1 is a diagram illustrating a circuit for compensating for anode potential variations and Fig. 2 is a diagram of a modified circuit.

In Fig. 1, reference character 1 denotes a thermionic tube comprising a cathode 2, a control v grid 3, a screen grid 4 and an anode 5. The

' anode is connected through a resistance 6 to the positive pole or" an anode voltage battery 7 whose negative end is connected to the cathode. The

screen grid is connected to the anode through a resistance 8. By a proper choice of the size of the resistances 6 and 8 the anode voltage and the screen grid voltage may be adjusted to the required value. The alternating currents set up in the screen grid circuit are lead to the cathode through the condenser 9.

If the anode direct current increases in this tube then a large voltage drop through the resistance 6 is brought about thereby. This entails a drop of both the anode and the screen grid voltages which results in a decrease or" the anode current. Altogether, a practical constant anode direct current may be achieved in this manner. However, this circuit arrangement has the drawback that as to alternating current, the impedance of the output circuit is reduced since it has connected in parallel to it a series connection of a resistance 8 and a condenser 9, the latter having such a value that it practically produces a short circuit for alternating current. Due to this the amplification of the tube is highly reduced.

In Fig. 2 this drawback is avoided by connecting the screen grid to the source of anode voltage through a resistance and part of the impedance inserted in the anode circuit. In Fig. 2 the screen grid is conn cted to a point 10 of the resistance 6 through a resistance 8. The variations in the direct current are neutralized by variations in the screen grid voltage which are caused by the voltage variations occurring in the portion 10, 11 of the resistance 6. It has been found that these variations ensure a suihciently constant anode direct current. For alternating current, however, the conditions have become much more favorable. In this case the anode impedance is formed by the resistance 6 and the series connection of the condenser 9 and the resistance 8 which connection is mounted in parallel to the portion 10, ll of the resistance 6.

Consequently for the same values of the resistances in the case of Fig. 1 and Fig. 2, the case of Fig. 2 will give a greater total impedance in the anode circuit, and, consequently a greater amplification too. Moreover, the resistances used in Fig. 2 for the same anode and screen grid voltages may be larger than in Fig. 1. This will be better understood by means of the following example. If, for instance, the available anode voltage is 200 volts, whereas the required anode voltage is 100 volts and the required screen grid voltage 50 volts, it being supposed that the average anode current is l milliampere and the average screen grid current 0.3 milliampere, then in the case of Fig. 1 the resistance 6 becomes 77,000 ohms, the resistance 8 becomes 170,000 ohms, i. e. for alternating current the total anode impedance corresponds to 53,000 ohms, it being supposed that the condenser 9 so large that it constitutes a short circuit for alternating current.

In the case of Fig. 2, however, the resistance 6 becomes 86,000 ohms of which the part 10, 11 is 46,000 ohms, Whereas in this case the resistance 8 amounts to 300,000 ohms. This corresponds in the aggregate to an anode impedance of 80,000 ohms. From this example it will be appreciated that a great magnification is achieved thereby. The advantage becomes still greater if the screen grid voltage with respect to the anode voltage is larger than in the case referred to above.

It may be adequate to insert another resistance in the circuit arrangement shown in Fig. 2, said resistance being connected in parallel to the condenser 9, especially in the presence of materially differing grid current for the various valves. Due to this, however, the amplification is slightly reduced.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be made without departing from the scope 110 of my invention as set forth in the appended claims.

What I claim is:

1. In combination, a source of signal energy, a thermionic tube having output and input circuits, a screen grid tube between the source and said input circuit, a source of anode potential for the screen grid tube, a coupling resistor in the anode circuit of the latter, and means connecting the screen grid to an intermediate point on the coupling resistor.

2. A wave repeater system comprising a space discharge device having cathode, anode and grid electrodes, an input circuit connected between said cathode and a grid electrode, adirect current path between said cathode and said anode, said direct current path including a resistance, and a direct current path between said cathode and a grid electrode including a resistance separate from the first mentioned resistance and a portion only of said first mentioned resistance.

3. A wave repeater system comprising a space discharge device having cathode, anode and grid electrodes, an input circuit for said space discharge device, a source of potential, a resistance having one end connected with the positive side of said source of potential and the other end connected to said anode, and a direct current connection from a point on said resistance intermediate its ends to a grid electrode of said space discharge device.

4. A wave repeater system comprising a space discharge device of the type having anode, cathode and grid electrodes, an input circuit for said space discharge device, a source of potential, resistance means, a direct current connection from a point on said resistance means to the positive side of said source of potential, a direct current connection from another point on said resistance means to said anode, and a direct current connection from a grid electrode of said device to a point on said resistance means intermediate the points connected to said anode and to said source of potential.

5. A wave repeater system comprising a space discharge device of the type having anode, cathode and grid electrodes, an input circuit for said space discharge device, a source of potential, a direct current path from the negative side of said source of potential to said cathode, a direct current path from the positive side of said source of potential to a control electrode of said device including resistance means, and a direct current path from an intermediate point on said resistance means to said anode.

6. A wave repeater system comprising a space discharge device of the type having anode, cathode and grid electrodes, one of said grid electrodes being a screen grid and another being a control grid, input circuit connections extending between said cathode and said control grid, a direct current path between said cathode and said anode, said direct current path including a source of potential and an impedance, a direct current path between said anode and said screen grid, the last mentioned direct current path including a resistor and a portion only of said impedance, and acapacitive reactance element connected between said screen grid and said cathode.

HERRE RINIA.

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