US1971894A - Broadcast receiver apparatus - Google Patents

Description

Aug. 28, 1934. G. ANDERS BROADCAST RECEIVER APPARATUS Filed March 23, 1929 I avwemto'c I GUIDO ANDERS $51, 1 5 flame/1,

Patented Aug. 28, 1934 Guido Anders, Berlin, Germany, assignor to Allgemeine Elektricitats-Gesellschaft, Berlin,

Germany, a corporation of Germany Application March 23, 1929, Serial No. 349,283 In Germany April 20, 1928 2 Claims.

This invention relates to electric phonograph devices of the type in which the mechanical vibrations of the needle of a pick-up device are converted into electrical vibrations which are in turn amplified and converted into acoustical energy. More particularly this invention relates to the circuit for amplifying the electrical vibrations, and to the use of an ordinary radio receiver amplifying circuit for such a purpose.

, In the mechanical talk ng machine or phonograph, the sound waves recorded upon the disk are converted directly into acoustic energy by the agency of a sound box. In the electric phonograph, on the other hand, the sound Waves are first changed by an electric pick-up device into electrical energy, the latter being then amplified, and finally fed to a loudspeaker which again converts the electrical energy into acoustic energy. Inasmuch as the electric phonograph possesses the merit of furnishing a more faithful reproduction than the mechanical machine, the general tendency in the recent past has been to replace mechanical phonographs by electric ones.

In this connection the question has arisen as to how an ordinary broadcast receiver could be used for the amplification of audio or musical frequencies. amplification, the operation of a broadcast receiver is usually to demodulate the radio frequency oscillations in an audion and to feed the ensuing audio frequency oscillations to the amplifier. One of the audion tubes thus fulfills two functions, i. e., it acts as a rectifier (grid current rectification) and simultaneously as an amplifier. In the amplification of audio-frequency oscillations of the kind produced by the pickup or contact, it is of course, of advantage to utilize the detector tube of the receiver also as an amplifier. This, according to previous practice, has

' 9; been possible only by providing various connections and switches for supplying the grid of the rectifying audion tube with a negative bias potential of the proper value for amplifying purposes, and by then feeding the audio frequency oscillations to the new grid circuit.

The solution to this problem, as disclosed in the present invention, namely, to use a broadcast receiver apparatus also as an amplifier for audio frequencies distinguishes itself by its great sim- .0. plicity. According to the present invention, two terminals are provided on the outside of the set which are adapted to receive the leads of the electrical pickup of the phonograph by means of plug sockets or the like. One of these leads is '55iunited with the grid of the detecting or rectify- Disregarding the radio frequency ing audion, and the other one with the gridbiasing potential.

The accompanying drawing, by way of example, shows diagrammatically one embodiment of a broadcast receiver according to this in-. vention.

0n the outside of the apparatus set, say, on the mounting plate, the two terminals 1 and 2 are provided. These terminals may be of the socketand-plug or any other suitable type. Terminal 6 l is connected with grid 3 of the detecting audion tube 4 and the terminal 2 with the grid biasing potential of the three-stage apparatus. A pickup device is illustrated diagrammatically at 5.

When using the set for amplification in com- 7.0 bination with the electrical phonograph, no changes in the circuit arrangement or the like are necessary; indeed, all that is necessary is to unite the leads of the pickup with terminals 1 and 2. The grid leak need not be removed inasmuch as it is high compared with the pickup and the circuit elements of the volume regulator. Hence, in order to use a broadcast receiver as an audio frequency amplifier, it is not necessary to make any changes in the circuit but only to provide two terminals in the set, and to connect these terminals with the receiver circuit in the manner hereinbefore described. By means of these connections, the grid of the detector tube which is normally biased by the proper potential for rectification, is provided with a new biasing .potential of the proper value for amplification without in any way changing the original circuit connections.

I claim:

1. In a signalling circuit an electronic tube arranged to normally act as a detector said tube being provided with an input circuit connected across the input elements thereof and an output circuit connected across the output elements thereof, an amplifier tube provided with an input circuit connected across the input elements thereof and an output circuit connected across the output elements thereof, a single source of space current for both said tubes and connected in both said output circuits, a bias resistor common to said two output circuits and the input circuit of the amplifier tube for providing the input element of said tube with a bias potential dependent upon the fiow of current through the resistor, a phonograph pick-up element including a pair of terminals and circuit connections for connecting said pick-up element and said bias resistor in series acrosslthe detector tube input circuit whereby said detector tube becomes biased to operate as in series and said input circuit also including said resistor whereby the amplifier tube is provided with a bias potential dependent upon the flow of current through the resistor, a phonograph pickup device and a circuit arrangement for connecting said phonograph pick-up device across theinput circuit of said detector tube, said circuit arrangement including said resistor whereby the first named tube is biased to act as an amplifier tube whenever the phonograph pick-up device is connected across the input circuit thereof.

GUIDO ANDERS.

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