US1985519A

US1985519A - Vacuum tube circuit

Info

Publication number: US1985519A
Application number: US580020A
Authority: US
Inventors: Ruben Samuel
Original assignee: Individual
Current assignee: Individual
Priority date: 1931-12-10
Filing date: 1931-12-10
Publication date: 1934-12-25
Anticipated expiration: 1951-12-25

Description

DeC. 25, 1934. 5 RUBEN VACUUM TUBE C IRCUIT Filed Dec. 10,- 1931 FIG.1.

INVENTOR- M BY HIS ATTORNEY- Patented Dec. 25, 1934 UNITED STATES PATENT OFFICE 6 Claims.

elements and to the connections of their elements in an electrical circuit. It is an improvement upon the arrangement described in my United States Letters Patent 1,815,931, the improvement more specifically being in respect to the structure of the tube and to the method of obtaining grid bias potentials. The object of this invention is the provision of a vacuum tube having high sensitivity and high power output, also means for obtaining grid biasing without the use of an extra source of potential for this purpose.

Broadly, the invention consists of a vacuum tube employing plural sets of elements, preferably in parallel arrangement, one set being connected to the input circuit and another to the output circuit and so interconnected that the latter produces an amplified response to the energy applied to the input electrodes of the first or controlling set of elements, the grids of the two sets having a predetermined inter-relationship in respect to the number of turns of each and the space separating them from their respective cathode elements. With a certain critical relationship established, maxima in sensitivity and power output are reached. By means of the arrangement of these sets of elements, high current amplification is efiected through the control of the electron discharge to the anode of one set of elements by the cathode-anode discharge in the other or control set of elements, and by the parallel arrangement of the sets of elements, inter-element current leakage is minimized.

My patent describes a tube in which there is a direct internal connection between the cathode of the input set of elements and the grid of the output set of elements. By the terms of this invention this connection is external to the tube and the grid biasing potential is obtained directly from the plate current supply circuit instead of from a separate source of potential.

This tube utilizes the current changes produced in the plate circuit of one set of elements when its grid is positively biased by the output current of the plate circuit of another set of elements; that is, by that set of elements to the grid of which the input or controlling potential is applied.

As set forth in my said patent, for a maximum output, the fundamental requirement is that the amplification factor of the controlling set of elements to which the input potential is applied,

elements, the grid of which is normally positively biased by the plate current 01 the control set of elements, so that the device operates by changes of positive bias potential or by the plate current changes in the first or controlling set of elements. For this the impedance of the plate circuit of the controlling set of elements should bear a definite ratio to that of the input grid and cathode impedance of the output set of elements. To secure this arrangement the grid of the controlling set of elements is preferably placed more closely to itscathode than the other grid to its cathode, also having a greater number of turns than the grid of the other set of elements. For such maximum power output and power sensitivity the product of the number of turns of the grid of the control set of elements about its adjacent cathode and the diameter of the grid coil is preferably in a substantially fixed ratio to the product of the number of turns of the grid of the second set and the diameter of that grid coil, as more deflnitely indicated below.

In a practicable combination of elements in tubes of the commercial type capable of having a transconductance of 25,000 microhms, after wide experimentation in varying the grids in respect to their diameters and number of turns, when using nickel cathode tubes of 0.065" diameter coated with barium-strontium oxide, and tungsten heater wire, 0.006" in diameter, coated with aluminum oxide by an oxychloride reaction, the best results were obtained with .0045 molybdenum wire grids of the following specifications:

Input setcoil diameter 0.110"; turns 56 per inch of cathode length.

Output set-coil diameter 0.150"; turns 40 per inch of cathode length.

It will be noted that the product of grid turns per inch and the diameter of the coil for a tube of maximum sensitivity is about the same for both input and output sets of elements. The anodes were made up of plates of carbonized nickel 1" long in 3%" cylinders; the electrical dimensions being five volts and 1.75 amperes heater power, the plate potential 250 volts; positive bias output grid control current 4 milliamperes--normal output plate current thirty milliamperes; negative control grid bias voltage 5. Undistorted watt output is 2.5. The negative potential to reduce the normal output plate current twenty volts is applied through a 20,000 ohm resistance. This is varied with the use to which the tube is to be applied.

The amplification characteristics of the combination are especially suitable for the operation of relays by direct current potential because of the wide plate current changes occurring with small input grid potential variations.

A plate current change caused, for instance, by a change of the input potential of the control grid, produces a change in the positive potential applied to the normally positively biased output grid element; it causes a large reduction in the space charge of the output circuit and a plate current change in the output circuit. Thus, a variation of one volt in the potential of the input grid gives a twenty-five milliampere change in the output plate circuit. The geometrical relation of the grids in their respective sets of elements, to afford the most efficient combination of elements, is described specifically in respect to a tube containing two sets of elements; but this relation between the control elements also holds in respect to the combination in which the sets of elements are in separate tubes as shown in my prior and copending application bearing Serial Number 553,052, filed July 25, 1931.

In some instances where separate and insulated sources of potential are available the cathodes may be directly and independently heated instead of by indirect means as here indicated, and they may be of the filament type.

By my improved arrangement, to obtain the necessary bias potential of the grid of the input set or group of elements, a resistance is connected in series with the cathode of that set and the grid of the output set of elements, and a condenser is shunted across it. And the return lead from the grid of the input set, for example from a transformer, is connected to the output grid and series resistances instead of with the cathode as shown in the patent. By this means a negative grid bias potential is obtained without the use of a separate source of direct current potential which is an important factor in the design of a vacuum tube circuit to be operated by a commercial lighting current.

By this arrangement also another negative bias is applied to the output grid which serves to reduce the output plate current when the control plate current is reduced to a negligible amount. This output grid potential is obtained by inserting in series with the cathode of the output set of elements a fixed resistance and condenser. The potential drop is applied by means of a series resistance to the grid element of the control grid. The efiect of this negative potential is had only when the potential drop between the cathode and grid elements, due to the plate current in the control grid, is less than the series resistance drop of potential. Thus, the unbiased plate current of the output tube is reduced to a lower value. When the plate current in the control tube rises, the bias potential is overcome and the output plate current rises, and there is a more efllcient operation, with a material increase in the range of operation in terms of power output and the normal output plate current required.

The invention is illustrated in the accompany ing drawing, in which 7 Fig. 1 is a circuit diagram showing a complete network for practicing the invention including a vacuum tube employing plural sets of elements.

Fig. 2 is a cross-sectional view of the tube structure.

For a better understanding of the invention reference is made to the accompanying drawing of one embodiment therof.

Referring to Fig. 1, the cathode 1, grid 2 and plate 3 are the control or input set of elements,

having leads at 5, 6 and '7 respectively. The cathode is, grid 2. and plate 3a are the output set of elements having leads at 5a, 6a and 78 respectively. The insulated wire heater elements are 4. and 4a supported on leads 8 and 8B. respectively. The glass spreader 9 assists in supporting both sets of elements so as to avoid vibration eflects. Connected between cathode 1 and grid 2a is resistance 14 which is shunted by condenser C. The input device such as transformer 1011, is connected to input grid 2 and resistance 12, grid 2a being connected so as to be negatively biased. The drop of potential is due to resistance 13 shunted by C1 in series with output cathode 19.. The resistance causes the drop of potential across it which is applied through a series resistance 12, of 20,000 ohms, which negative potential reduces the normal positive potential obtained from the input plate current set and negatively biases the output grid only when the plate current of the control set of elements is of very low value or at zero.

The translating device 15, such as aloud speaker, is connected in the output plate circuit. The potential for operating the elements is obtained from any of the commonly applied sources of sup- .ply, such as the combination wherein tube 1'7,

with cathode and

anodes

18 and 19, is the rectifier, C2 and C3 the filter circuit condensers, and 16 the necessary inductance. The transformer, with various

secondary windings

21, 22 and 23, supplies the necessary cathode heating and plate potentials.

The method of obtaining the various grid bias potentials and the connection of the element,

while shown in a single tube arrangement, is also applicable where the input and output elements are in separate tubes as shown in my co-pending application bearing Serial Number 553,052 filed July 25, 1931.

What I claim is:

1. In a vacuum tube circuit an electrical discharge device comprising an evacuated envelope containing a cathode, a grid and a plate element, another cathode insulated from the first mentioned cathode, grid and plate element insulated from the first mentioned plate element, said second mentioned grid being connected with the first mentioned cathode through a series resistance element.

2. In a vacuum tube circuit, an electrical discharge device comprising an evacuated envelope containing a cathode, a grid and a plate element, another cathode insulated from the first mentioned cathode, grid and plate element insulated from the first mentioned plate element, the first mentioned set of elements being mounted in a position parallel to the second mentioned set of elements, the cathode of the first mentioned set of elements being connected to the grid of the second mentioned set of elements through a resistance element, so as to be at a potential difference with said grid.

3. In a vacuum tube circuit, an electrical discharge device comprising an evacuated envelope containing an input set of elements consisting of a cathode, a grid, an anode and a heater for heating the cathode, and an output set of elements consisting of a cathode insulated from the first mentioned cathode, a grid and an anode insulated from the first mentioned anode and a. heater for heating the cathode, the two sets of elements being mounted in parallel positions and the output grid being electrically connected with the input cathode through a series connected resistance.

4. In avacuum tube circuit an electrical discharge device comprising an evacuated envelope containing a triode consisting of a cathode, a grid and an anode and another triode consisting of a cathode, a grid and an anode, the cathodes being insulated from each other and the anodes being insulated from each other, the grid in the second mentioned triode being connected with the cathode in the first mentioned triode through a series resistance, the amplification factor of one triode being higher than the amplification factor of the other triode.

5. In a vacuum tube circuit an electrical discharge device comprising an evacuated envelope containing a triode consisting of a cathode, a grid and an anode, and another triode consisting of a cathode, a grid and an anode, the cathodes being insulated from each other and the anodes being insulated from each other, the grid in the second mentioned triode being connected with the oathode in the first mentioned triode through a series resistance, the grid of the control triode having a greater number of turns and being closer to its cathode than the grid of the other triode in respect to its cathode.

6. In a vacuum tube circuit an electrical discharge device comprising an evacuated envelope containing a triode consisting of a cathode, a grid and an anode, and another triode consisting of a cathode, a grid and an anode, the cathodes being insulated from each other and the anodes being insulated from each other, the cathode in the first mentioned triode being connected through a resistance element with the grid 0! the second mentioned triode, the grid of the control triode having a greater number of turns than, and being closer to its cathode than the other grid, the product of the number of turns of wire 0! the control grid per unit length of its cathode multiplied by the grid diameter being substantially the equivalent of the product of the number of turns of the other grid multiplied by its diameter, the number of turns being less than the number of turns of the 20 control grid.

SAMUEL RUBEN.