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RADIO BROADCAST ADVERTISER
503
FEATURING THE NEW GENERAL RADIO DOUBLE IMPEDANCE
A NEW Amplifier Unit
which provides for FAITHFUL REPRODUCTION of
FULL ORCHESTRATION
Type 373
Double
Impedance Coupler
Price $6.50 (2 required)
373
373
Type 285D
Audio
Transformer
Price $6.00
(1 required)
285D
Type 387 A
Speaker
Filter
Price $6.00
(1 required)
387A
Type 349 UX Tube Socket Price 50c (3 required)
C BATT.
A BATT.
135 B BATT.
Type 401 Rheostat 6 ohms Price $1.25 (1 required)
A GRAPHIC REPRESENTATION OF
Vocal and Instrumental Tones
as they are amplified by the Type 373 Double Impedance Coupler -ORCHESTRAL RANGEVOCAL RANGE
300 1000 FREQUENCY
10000
The extent is its range of even amplification is from appreciably below 6o cycles to over 10,000 cycles, with a gradual downward deviation of slightly less than 7% between 100 and 400 cycles. This deviation in an otherwise perfect amplification curve is so slight as to be practically negligible, because the ear of the average individual cannot; detect a variation of intensity of much less than 25%.
The amplification curve, in fact, compares favorably with that generally obtained with resistance coupled systems which have the disadvantage of large sacrifices of plate voltages.
The above circuit diagram shows a combination of two stages of double inv pedance coupling and one stage of transformer coupling with speaker filter. While the use of double impedances is not new in principle, the General Radio Type 373 Double Impedance Coupler is unique in design and per' formance. To facilitate installation, the complete unit, consisting of two impedances and a fixed condenser, is contained within a metal shell. It is connected in an audio amplifier circuit in precisely the same manner as a transformer. The amplifier combination shown above may be readily adapted to any standard manufactured or home constructed receiver, and will produce a very noticeable improvement in tone quality. Its high and even amplification extends over the range of FULL ORCHESTRATION. The deep bass tones of the kettle drum are brought out in full timbre as are the shrill notes of the flute. The range of the human voice is covered with pleasing clarity.
The above amplifier combination has the further advantage that it may be used with the General Radio Type 405 Raytheon Plate Supply Unit. By substituting two Type 373 Units for the transformers of a two stage transformer coupled amplifier the above combination may be completed and proper plate voltages provided by using the General Radio Type 400 Power Amplifier and Plate Supply.
As\ your dealer or write for folder 373
GENERAL RADIO CO.
Cambridge, Mass.
PARTS AND ACCESSORIES
The General Radio Company has endeavored to make it possible for the experimenter to obtain its products with minimum of effort. A careful selection of distributors and dealers has been made. They are best suited to serve you. If, however, you are unable to obtain our products in your particular locality, they will be delivered to you, post paid, direct from the factory upon receipt of list price.