US1926860A - Amplifier system - Google Patents

Description

p 1933. A. K. ROSS 1,926,860

AMPLIFIER SYSTEM Filed April 25, 1 2

I INVENTOR ATTORNEY Patented Sept. 12, 1933 UNITED PAT AMPLIFIER SYSTEM Allan K. .Ross, Rochester, N. Y. Application April 25, 1925.}Serial No. 25,780

5 Claims. (01. 250- 40 This invention relates to amplifier systems and in particular to amplifier'systems foruse. in amplifying radio signals. v.

In certain types of amplifier systems it has been customary to employ aplurality of tuned amplifying stages. gives excellent results, is expensive to manufacture since it requires a variable condenser for 1 each stagerwith the result that there'are at least 7 as many controls as there are amplifying stages,

over a wide portion of the range of frequencies the stages are not in resonance so that accurate tuning does not take place. In order to overcome this ditficulty it has been proposed to provide one master control for roughly tuning each of a plurality of stages, and further to, provide an individual. Vernier control for the'accurate tu'ningof each stage. The necessity for such Vernier controls defeats the purpose of such a master control arrangement.

In accordance with the present invention it is proposed'to obviate the necessity of providing a variable condenser and an individual control therefor in each, amplifying stage and to avoid the undesirable features of the master controlled system by providing a single variable capacity common to a plurality of amplifying stages whereby all of the stages may be simultaneously and accurately tuned by the use of a single control.

The drawing represents the invention applied to a tuned radio frequency amplifying radio re ceiver, although it will be understood that it may be used with audio amplifying systems or in any other arrangement wherein a plurality of stages are tuned to the same or to an approximately:

the input circuit of a thermionic device or vac-' .uum tube 8. This input circuit extends from 5 the grid 9 of this vacuum tube throughv the sec- Such an arrangement, while it conductor 17 to the filament 23.

, ondary'winding '7, the potentiometer 10 to the filament 11. with the common variable condenser .13 is con-' The fixedcondenser 12 in series nected in multiple across the input circuit and p the capacity of the fixed'condenser 12 with that of the variable condenser 13 and the inductance of the secondary coil '7 serve to tune the input circuit just described. The output circuit of the thermionic device 8 extends fromtheplate 14 thereof through the primary winding 15 'of a second radio "frequency transformer throughthe high potential B battery 16 and common conductor 17Ito the filament system including the low voltage A battery 18 by which the filaments of the various thermionic devices are heated.

The primary winding 15 as in the case of the first primary winding 6 is closely coupled to the secondary winding 19 which is connected in the input circuit .of a second thermionic device 20 which functions as a second stagefor amplifying 7571 radiofrequency currents. This input circuit may be traced from the grid 21 through the secondary winding 19 and through the potentiometer 10 to the filament system including the common conductor 17 and the filament 23. A fixed condenser 8075! stage includes the plate 24, primary winding 26 of a third radio frequency transformer, conductor 25, the high voltage battery 16, the common The primary winding 26 ofthis third mentioned transformer is closely coupled to the secondary winding 2'7 thereof which is included in the input circuit of a detector tube 28. This input circuit is likewise tuned'by a fixed condenser 28 connected in series with the common variable condenser 13 across the input circuit in multiple with the secondary winding 27. It will be noted that this input circuit includes the well known grid condenser 29 and the grid leak 30 to control the potentials present on the grid 31 of the detector. The filament 32 of the detector is heated from the battery 18 as in the case of the thermionic devices 8 and-20, but in this instance a variable rheostat 33 for controlling the heating of this tube is provided instead of the fixed resistance controls 34 5 and 35 of the other filaments. The output circuit of the detector tube as herein shown extends from the plate 36 to an indicating device 37 which may be in the form of telephone receivers or a loud speaker. When these devices are used a well known by-pass condenser'38 may beemployed. It will be understood that the indicating device 37 and the by-pass condenser 38 may be replaced by the primary winding of an audio transformer the secondary winding of which is connected in the input circuit of an audio ampli-' fying thermionic device.

From the foregoing it will be understood that the input'circuits of the thermionic devices 8 and 20 and the detector tube 28 are all tuned to the frequency of the incoming signal by means of the common variable condenser 13 which is connected in series with the fixed condensers 12, 22, and 28. All of the mentioned fixed condensers are of the same capacity and the inductances of secondary windings 7, l9, and 2'7 are all equal,

so that any change made in the capacity of the;

variable condenser 13 causes a corresponding change in the effective capacity connected across the mentioned windings which changes the tuningof each input circuit and insures that, all circuits are tuned to the same frequency over the entire band of wave lengths covered by any combination of inductance and capacity.

It has been found in practice that such a set is especially easy to operate since it requires the adjustment of only one variable condenser and the possible adjustment .of the potentiometer 10 in the event that there is any tendency for undesirable oscillations in the receiver. 4

'While the invention has been disclosed as a radio frequency amplifier in a radio receiver, it

will be understood that it may be employed for riable capacity.

, ductive reactance and a capacitive reactance conneted in eah stage, and a variable condenser in series with a, plurality of said capacitive reactances for simultaneously tuning said stages.

3; The method of tuning a multi-stage thermionic amplifier having fixed inductive reactance and fixed capacitive reactance in each stage which consists in adding a variable reactance supplementing said fixed reactance. r

4. The method of tuning a multi-stage amplifier havinginductance and capacity in each stage which consists in supplementing the capacity in each stage by common variable capacity. 5. The method of tuning a multi-stage amplifier-having inductance and capacity in a closed net-work in the input circuit of each stage which consists in supplementing the capacity in the closed net-work of each stage by common va- ALLAN KJRO SS.

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