US2068752A - Main operated voltage amplifier - Google Patents

Description

Jan/26,1937; s, L EWE ETAL 2,068,752

MAIN OPERATED VOLTAGE AMPLIFIER Filed Jan. 20, 1930 1 gnaw/(4770M $20-04? 0/52 100 Jnuenfar:

Patented Jan. 26, 1937 STATS PA'E'E T @FFHQE Berlin, Germany; said to Radioaktiengesellsch Stegiitz, Germany, a co Von Ardenne assignor aft D. S. Lcewe, Berlinmpany of Germany Application January 20, 1930, Serial No. 422,212 In Germany January 22, 1929 2 Claims.

The resistance amplifiers used at present are generally provided with valves having an amplification factor of about 25 to 33-and plate resistances of some megohms. The voltage supplied to the plates of the amplifier will frequently be only volts and hardly ever more than volts.

Owing to the fact that the plate resistances cannot be chosen over a certain value on account of the weakening effect of the unavoidable capacities noticeable already at low frequencies, the amplification of a voltage amplifying stage cannot be increased at will, by increasing the amplification factor. If the plate resistance and the voltage in the plate circuit do not exceed a certain maximum, the amplification increases only to a certain point with the increase of the amplification factor whilst when the amplification factor is further increased, the amplification is considerably reduced. In voltage amplifiers operating at normal voltage and with plate resistances of an order of not more than 10 megohms, it would be injurious to apply an amplification factor above 100.

The invention overcomes this difiiculty by using very high plate potentials. If the plate potential is increased and if the amplification factor and the plate resistance remain constant, the amplification increases only slightly. But if the plate potential is increased and that amplification factor applied which is optimal for the plate potential in question, the result is a very considerable increase of the amplification to be optimally attained. You may reckon that the amplification may be somewhat doubled if the plate potential is quadrupled and the amplification factor simultaneously doubled.

If batteries should be used to get a high anode potential difliculties would arise with regard to insulation. Furthermore such batteries are to be avoided for saving in space and its attendance and control would make difi'icult the handling of the plant.

Our invention does not sufier from these disadvantages. According to our invention the alternating voltage of lighting mains is stepped up to a high voltage which after rectification and the necessary filtration is supplied to the resistance amplifier.

The secondary side is, for instance, stepped up to 1000 to 2000 volts.

Plate resistances of 8 to 10 megohms may be used. If sufficiently high voltages are used and if the amplification factor of the valves is simultaneously increased to, say, 2000 the amplification to be obtained in a voltage amplification stage 5 may be 1000 or more so that, by applying the invention, for many purposes one voltage amplification stage only is sufiicient.

For the power amplification stage higher currents at ordinary voltages are preferable. Ac- 10 cording to the further object of our invention such a stage is therefore not connected with the high voltage rectifier. It is advisable to use a separate transformer with special rectifier and filter for the power amplification stage.

Our invention may be best understood with reference to the accompanying drawing.

The figure shows a diagrammatic representation of our invention. R1 is a voltage amplification stage, R2 a terminal repeater stage. 5 the 20 coupling condenser, E the coupling resistance. The illustration shows further that part of the battery eliminator consisting essentially of transformer l2 and rectifier l3, which supplies the direct voltage of 1000 to 2000 volts terminal. That 25 part of the battery eliminator which supplies the power stage, is not drawn, but only indicated by the terminal of 150 volts. To that terminal the 150 volt-line leads from the plate of the power valve across the loudspeaker L.

We claim:

1. In an electric amplifier a tube of an amplification factor of more than 100 having cathode, grid and plate, a source of direct current of at least 1000 volts, and an anode resistance in the 35 order of 8-10 inegohms connecting said anode of said tube to the positive pole of said source.

2. In an electronic amplifier a tube of an amplification factor of more than 100, a second terminal tube, both tubes having cathode, grid and 40 plate, a source of direct current of at least 1000 volts, a coupling resistance in the order of 8-10 megohms, connecting the plate of the first tube to the positive pole of said source and a coupling condenser connecting the plate of the first tube to the grid of the second tube, the grid of the first tube being connected to the input and the plate of the second tube being connected to the Output of the amplifier.

SIEGMUND LOEWE. MANFRED VON ARDENNE.

Images