US1892924A - Amplifying arrangement with tubes connected in counter cadence - Google Patents

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Fan 3, @339 J. BABLER 1,892,924

AMPLIFYING ARRANGEMENT WITH TUBES CONNECTED IN COUNTER CADENCE Filed Sept. 11. 1929 iNVENTOR JUSTUS BABLER Patented Jan. 3, 1933 UETED STATES JUS'IUS BABLER, 0F BERLIN, GERMANY, ASSIGNOR TO ALLGEMEINE ELEKTRICITATS- GESELLSCHAFT, OF BERLIN, GERMANY, A CORPORATION OF GERMANY AMPLIFYING- ARRANGEMENT WITH TUBES CONNECTED IN COUNTER CADENCE Application filed September 11, 1929, Serial No. 391,760, and in Germany October 13, 1928.

In tube amplifiers which are fed from a direct current network the various potentials, such as the heating, plate and grid voltages of the tubes are obtained by means of a voltage dividing resistance connected parallel to the direct current network. To eliminate the commutator noises it is necessary to include filter chains in the supply circuits. It must be noted, however, that the necessity of maintaining a suficiently high direct current voltage beyond the filter chains requires the direct current resistances of the choke coils to be very low. Consequently choke coils and condensers of a very large size must be employed the cost of which may, depending on the desired degree of choking, eventually exceed the cost of the amplifying device proper.

This invention is concerned with a circuit arrangement designed to compensate the commutator noises of a tube amplifier the two tubes of which, connected in counter cadence,

are fed from a direct current net by way of a voltage dividing resistance. According to the invention the grid and plate potentials of one tube are selected according to the operating conditions whereas the grid and plate potentials of the other tube are so adjusted to compensate or eliminate the plate current variations caused by the net noises. lVith this circuit arrangement the insertion of filter chains as an expedient for the choking of net noises is completely dispensed with. The elimination of the choke coils and condensers which would have to be employed with filter chains makes the construct on of such an amplifier very simple and cheap.

The operation of this invention will be explained with reference to the attached drawing. The drawing shows an example in which the compensation of net noises is achieved by adjusting the grid voltage of one tube. In the drawing the notations for the various potentials are marked by arrows and numbers to distinguish them from the designations of the circuit elements.

The feeding of the two tubes a and 1) connected in counter cadence takes place by way of a voltage dividing resistance connected parallel to the direct current network and consisting of the component resistances 0, d

and c. On the component resistance 6 there is a shiftable contact for the biasing grid potential of tube a and a contact for the biasing grid potential of tube 6. Of the input transformer the drawing shows only the secondary windings f and 7 connected to the grids of tubes 44 and b respectively. The output transformer contains the primary windings g, g and the secondary windin h.

In the grid coils f, f potentials are induced whose electromotive forces 1 are in phase opposition. The electromotive forces 2 of tubes 0: and b are likewise in phase opposition. The primary windings g, g of the output transformer are connected in the same sense so that the electromotive forces 3 act in the same direction. This causes electromotive forces 4 to be induced in the secondary winding h.

Reversed conditions are obtained for the disturbing voltages caused by the pulsating potential at the voltage dividing resistance. Two kinds of voltage variations appear at this point, firsta pulsation of the grid potential 5 and, consequently, of the plate current, and second-a pulsation of the plate potential 6 and, as a result of this, also of the plate current. These pulsating voltages are co-phasal in regard to the tubes; however, on the primary windings g, g of the output transformer they have the opposite effect; due

to this fact the pulsations, provided they are of the same amplitude, cancel each other and no disturbing voltages are transmitted to the secondary winding h of the output transformer. The transformer constitutes, so to speak, a short circuit for these disturbing currents, and the tube phenomena follow the static characteristic. Thus the following equation holds true for each tube:

S=slope or steepness of the tube (the charu acteristic curve) K construction constant a 2 1' grid resistance R represents the total plate circuit resistance r =plate resistance.

As evident from a contemplation of the above given formula it is necessary, 1n order to compensate the disturbances, to make the A value of equal for both tubes. According to the invention this can be achieved by properly adjusting along the Voltage dividing resistance the contacts over which the tubes receive their respective grid or plate potentials. 7 It is, for instance, possible, with one tube at one half of its maximum steepness, to fix its biasing potential and vary the biasing potential of the other tube-so that the net noises are eliminated (compensated). I claim: v

v l; The combination of a push-pull amplifier, and a resistance network adapted to be connected'in parallel with a. direct current source, means for connectingthe filaments of said tubes in parallel with each other and with a portion of said network, means ?for connecting the anodes of said tubes to a point onsaid network and meansfor connecting each of the grids of. said tubes to difi erent predetermined points on said network.

2. The combination of a push-pull amplifier, and a resistance network adapted to be connected in parallel with a direct'current source, means for connecting the filaments of said tubes in parallel with each other and with a portion of said network, means'fo'r connecting the grids of said tubes to'a point on said network and means for connecting each of the anodes of said tubes to different predetermined points 011 said network.

3. In a thermionic relay device a pair of thermionic tubes having symmetrical input andoutput circuits, .a resistance adapted to I be connected in series with a source of pulsatlng dlrect current, means for connecting the cathodes of said tubes in parallel with 7 each other and with a portion of said resistance, means for connecting the anode 'c1rcults of sald tubes to a point on said series resistance, a connection between the control electrode of one of said tubes and a point on said resistance, and means for eliminating the efiect of any potential variations im-' pressed on said resistance from said source including, means to connect the control electrode of the other of said thermionic tubes to a movable point on said resistance.

JUSTUS BABLER.

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