The Birmingham age-herald., 1922-07-16
Uni-DirectionaI Current,

OhA-0tNccttOhut OurECuts
 Q. In reference to diagram In Radio Corporation catalogue of November 1. 1921, page ss. Showing standard wiring diagram for a detec- tor and two stages of audio-fre- quency amplification: This diagram and others show the Telephones" and "B' battery in the plate circuit of the last amplification tube. and my ques- tion is, what Is the kind of current that goes through the telephones? Is 1t direct current or intermittent flow and varying intensity or potential. or is it an alternating current of vary ing potential? Most local radio fans of good standing claim 1t can be no other than direct current. A few claim A. C., and have before me a diagram and explanation by an ex- pert showing small detector wiring diagram, using a 'bridging conden- ser" around the "B" battery, explain ing that "a condenser in such a posi- tion. in the radio circuit serves as a path of low impendence across the battery for the high frequency alter nations in the plate circuit" In the experimental work that l have done. for building data on loud speakers. the results all point to A. c. In other words, an experimental design theo- rized on basis of A. c. gives results and those built for D. c. do not. In the event that there are nook cups" that create a D. c. current through the phones and others they will create A. C., will you oblige by mentioning an obtainable circuit of each? W. F. R.
 A. The current which flows through a telephone receiver is a di- rect. pulsating current, corresponding to the group pulsations of audio-f fre- quency. It isn't, in actuality, strictly direct current. but a uni -directionaI current, 1t must be taken into con- sideration that the vacuum tube as a rectifier, does not rectify absolutely 100 per cent; and consequently there is an alternating current flow in the plate circuit back to the grid circuit and the bridging condenser assists the flow of this current. which aids in amplifying. I do not know of any hook-ups, other than the regulation vacuum tube diagrams.
 Notes on Short Wave Set
 o. I am located 50 miles from new York and Newark and my purpose Is to receive radio phone from 45 to 50 miles and radio-tele- graph signals from 475 to 500 miles With the object of soon adding two-tep amplifier hook-up, please advise me: 1. Should use . vario- meter or variocoupler! 1. If tho fixed condenser were eliminated would that add to or detract from the efficiency? 5. Please tell me exactly what battery voltage and amperage should be used. {. In the circuit of which battery is the rheo- stat placed? Would 2 potentiomete ter materially improve the clearness of signals? 5. Will the aforesaid bat teries permit the use of amplifiers without additional batteriesY Are rheostats necessary for the amplify- ing circuit? s. c.
 A. Use variocoupler-wave length range 15o to 600 meters. !. You will need fired condenser across the telephone leads. 8. Using the vacuum tube. you will need G. volt storage battery. anl if it Is
 your purpose to add ono or moro
 stages of ampiification I would sug-
 gest an So-ampere hour battery. Yyu
 will also need a "B" battery of z2A volts for the plate circuit of the vacuum tube. This Is dry cell battery made standard form. and will last approximately 1000 hours. {. The rheostat is placed in the stor- age battery circuit Tn se-ie with one of the filanent terminals of the vacuum tube. A potenticineter placed | across the storage battery VII ma terially aid in stabilizing the circuit. giving clearer signals. 5. You can use the above batteries for tho addi- tional amplifying stages. but 1t will be necessary to add separate rheo- stats for the amplifying tubes.
 Q.-I desire to build up . TO- ceiving set for reception of long wave length. as up to 2.6oo meters. using a standard variometer. vari-
 able condenser of OOH M. F. capac. | ity. and bank wound coil which am making. In regard to the coil described by you on June 25, when Ia the tapping point reached? I wish l to have 10 taps on the coil. Should the taps be taken on at -.e top wire
 of the bank or next to the tubel
 This information would help me