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Show I i TltfrtTr I 'Tilil' immsml) .vxza MMIi'i -Tjr- "" -..'"- A (Ed!td by O. Imilslai Wardruu. KdHor of Radio Merchandising.) CI CI CI j ( -B A 4590 t35 j Diagram Showing Amplifier Alono, Wired to Plug by Single Lead; Arrange- ment Suggested for Adding Resistance Coupling to Any Circuit. I Leslsianee-coiipled audio amplllica-tlon amplllica-tlon is meeting with popular favor wherever It has been tried. It reproduces repro-duces over tho entire scale without distort ion of any kind. Its only drawback Is that three stages are necessary nec-essary to produce the volume of two stages of transformer-coupled nmpliii-cation. nmpliii-cation. The diagram shows how a resistance-coupled amplifier can be added to any set. The coupling registers. Ul, 0f t he A. !'. amplilier are KiO.noO-ohm resistances. resist-ances. This value remains the same for all tubes (practically), as do the .000 mfd. coupling-isolating condensers, Cl. J he grid leaks, Ii2, K:i and R-t have respective values of 1 megohm, i megohm ant! i megohm. Tlie diagram shows the amplifier alone, wired to a plug hy n single lead, which arrangement is suggested for ndding resistance coupling lo any circuit. cir-cuit. Practically no knowledge whatever what-ever of tlie receiving circuit is necessary. neces-sary. Wire X should be tapped on 45 volts of B battery. After tuning in a station on telephone tele-phone receivers, tlie phones should be removed and tlie amplilier plugged Into the jack. If no signals are heard, the single wire leading to tlie plug should be transferred to the other plug terminal. When signals are being be-ing amplified, X should be varied over the B battery taps until tlie response Is the strongest without Impairing quality. Transformers Can Be Used. The amplifier should always be plugged Into the lowest stage jack on the receiver proper the jack that ordinarily or-dinarily gives the weakest response. Many neutrodynes are so arranged that at least one stage of transformer- coupled audio frequency amplification must be employed. This being the case, no more than two stages of resistance re-sistance coupling should he added. One extra step generally will suffice. Quality probably will not suffer through tlie single stage of transformer-coupled Intensification. Properly Prop-erly designed and operated, one transformer-coupled stage should be audi-tively audi-tively perfect. If the receiver to which yon contemplate con-template the addition of resistance coupling is a five-tube set, and four tubes are used (lighted) on the lowest low-est jack, it is an indication that one .transformer coupled stage is being employed. High Voltage Is Necessary. When in-putting from the detector tube, from 45 to 00 volts should bo applied to the plate of this bulb-compensating bulb-compensating as usual for the voltage drop across the coupling resistor in the plate circuit. No more than 90 volts should be Impressed on the r. f. circuit while 135 volts or more should be used on the a. f. amplifier. This last will function satisfactorily on 90 volts, though higher amplification is quite naturally secured on the increased voltage. When in-putting from a transformer coupled stage, the normal detector voltage should be used. If only two resistance coupled tubes are used, the leak values should be and megohm respectively. If a single stage Is employed the grid leak should be a 50,000 ohm resistance. re-sistance. The UV-201A. the C-301A and the DeForest DV-2 tubes will function satisfactorily In this amplifier. |