US1685253A - Double-grid thermionic tube - Google Patents

Description

Sit. 25, 1928.

M. VONARDENNE DOUBLE GRID THERMIONIC TUBE Filed Dec. 17, 1926 INVENTQR MANFRED VON ARDENNE BY 8% gw/W ATTORNEY Patented Sept. 25, 1928.

uNiTsD- STATES PATENT OFFICE.

mmrmi) voN ABDENNE, or BERLIN, GERMANY, ASSIGNOR To name oonrommron or AMERICA, A. oonronarron or DELAWARE.

DOUBLE-earn THERMIONIC TUBE.

Application filed December 17, 1926, Serial No. 155,544, and in Germany December 1, 1925.

It is known that tubes equipped with two (and, if desired, more grids) can be used in what is known as the space-charge and the protective grid Connection.

It is also known, that, according to the particular use ofthe tube, either. the one or the other kind of connection offers greater advantage. Examining the conditions for most favorable amplification of high-frequency alternating current,on the one hand, and low-frequency alternating current, on the other hand, it is found that one and the same tube is able to give optimum conditions for both services only by the adoption of a special form of construction. The two-grid tubes heretofore used either inspace-charge or protective grid connection, so far as their working characteristics are concerned especially the inverse amplification factor, are nothing but a matter of chance, so that, for instance, while they may be particularly adva'ntageous for audio-frequency amplificationin the so-called protective grid connection, they are unable to give at the same time optimum conditions for radio frequency amplification in the space-charge connection.

Now, the special type of tube hereinafter to be described is so designed that it happens to give best results for low frequency amplification in the protective grid arrangement,

- while offering most advantages for radio frequency amplification'in the space-charge connection. Optimum inverse amplification factor (Durchgriif) to be sure, is not a constant magnitude, although tests have shown that inside the customary broadcast wave range,

- i. e., between 200 and 800 meters approximately, an inverse amplification factor of 10% proves best. But an especially favorable audio-frequency amplification is obtained with the same tube in protective grid connection, with an inverse amplification factor of 1%. The construction of the tube will.

be described hereinafter in more detail.

As will be seen-: from what precedes, the most particularfeature of, the constructlon of the present tube-resides in that the same exhibits an inverse amplification factor of 10% when in space-charge connection, and an inverse amplification factor of 1% when arranged in protective grid connection.

. view of my tube and,

[In the accompanying drawing Fig; 1 shows somewhat diagrammatically -a elevat on .ner grid comprises13fturns, the outer one 18 turns, the wire diameter of both grids being about 0.2 mm. Y

Although the particular dimensions as hereinbefore indicated are merely indicated to attain the aim of the invention, the basic idea of the latter is more general. For, as could be shown theoretically, it is always possible to satisfy simultaneously two conditions with one two-grid tube, that is, a definite inverse amplification factor D1 with the tube arranged in space-charge connection, and another inverse amplification factor D also to be chosen ad lib., with the tube arranged in protective-grid connection, provided that D does not exceed D. The means adapted to insure the desired inverse amplification factors are themselves well know'n,

and they consist in variable relatix e grid and plate resistances, variable number of'diameters of grid wires, and other secondary and less important factors.

I Now, while in the conventional types of two-grid tubes, the: conditions as to in'verseamplification factor ratios between space-- charge and protective-grid connection were a mere matter of chance, these relations according to the present inventiom as above pointed out are to be chosen in such a manner that for the two modes of circuit arrangement and connection the working conditions of the-tubes are so that there result optimuni dimensions for the various fields of application. It is thus possible to make one and the same tube for different purposes, which" represents a great manufacturing advantage and also a sav ng in tubes, lnd'ecd, only oneloo half the number of tubesis' required since they'ar usable-for a two-fold purpose.

My tubes may be utilized for example, in a circuit of the type shown in Fig." 2. Radio ned circuit being :fed

across the radio frequency grid 2-and fila- -ircuit 7, potential vament 1 of im roved tube indicated by numeral 5 in-that gure. The radio frequency output of tube 5 is shunted across an audio frequency transformer '81by means ,of condenser 9 and is fed into a second tuned circuit 10, which in turn feeds a detector circuit 11. By means of audio frequency transformer 12, audio frequency variations and potentials are impressed across the grid '3 and filament 1 of my tube 5. The resulting amplified audio frequency current variations appearing in the plate circuit of tube 5 arev fed'by means of transformer 8 into a suitable sound producing device 13. In this manner myimproved tube is used both for radio frequency amplification and for low frequency amplification.

, I claim as my invention:

A thermionic tube comprising a straight filament substantially 2-centimeters long, a

pair of concentric coiled grids about the filamillimeters and having substantially 18- turns, the inner grid being adapted for caus 111g high frequency variations in the electron stream of the tube, and the outer grid being adapted for causing low frequency varia tions in the electron stream of the tube.

YMANFRED vON ARDENNE.

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