Show 71 am AV 0 rec ste 6 etc tull AS 54 1 46 PEI I 1 rig i A 8 A left circuit diagram which Is tho the principle of the right details of radio frequency coupling transformers Transform era all things considered ease of control simplicity of construction selectivity and range of reception the five tube tuned radio frequency set Is the most efficient hookup hook book up that has been developed tile the one stumbling block has haa been the proper means of controlling the oscillating characteristics of the tube Seve several riki means of doing this have been devised most ot of them effective but all hod had their drawbacks the recently described in the radio news and tested out la in that publications laboratories seems to be one of tile the best beat circuits yet offered the following description of this set ts ta taken from tile the radio news it Is well known that tant when several stages of radio frequency amplification are employed in radio receivers there la Is a tendency for self oscillation to occur in the circuits this la Is one due to the feeding back of radio frequency energy from the plate circuit cf a tube to the grid circuit of tiny any other tube or to its own grid circuit the feedback feed food back there are in general three ways waya of 0 preventing this feedback feed back bach viz the introduction tro of resistance into the oscillatory cill atory circuits neutralization of the tube capacity or magnetic coupling introduction tro luction into the circuits of electromotive forces which have a polarity or phase opposed to that of the incoming signals the last method to Is that employed in the sup erdyne receiver and la Is also the method which has been employed in this receiver there la is a difference however in the way in which to 0 U 4 MF P coo M F mr figa tho the receiver employs employ the above wiring diagram the he circuit stability Is accomplished fo for r in the aup sup erdyne this so called negative feedback feed back la is accomplished by coupling a coll coil in the plate circuit of f a stage to acollins a coil in the grid circuit whereas in the system the coupling Is between a coll coil in the filament circuit and the one in the grid circuit the fundamental circuit diagram to la shown in fig 1 here tho the common terminal the negative filament connection tion tiou Is bro broken lan and the feedback feed back coll coil connected acress the break the polarity of the feedback feed back coll coil to is to be made such finch that it will prevent self oscillation fig 2 shows the complete wiring diagram ortho set three such feedback colts colls are used one for tech each stage of radio frequency and the circuit one might ciblatt that by using BO many adymt able the operation ot of thil theace ellei would I 1 beckma very complicated bach ts Is not be found that hatow t of the food feed bftts colls coils can be left untouched once they are arc adjusted so BO that the number of tuning controls in the set la Is reduced to the three condenser dials and one dial for or adjusting the first feedback feed back coll coil or compensator the ide idea a Is th that atthe the second stage of RP amplification Is adjusted on the long waves wave so BO that as am the feed increases with the short abort waves there will be less tendency for oscillations that la Is the set Is tuned in on the longist longest wave it Is ili desired to receive say GOO meters and the second and third compensating colls coils adjusted careful y to the point at which howling just ceases after this they can be left alone for on all wavelengths wave lengths shorter than this were there will be less tendency for self belf oscillation to occur the amplification in these stages will always be high however in fact it will be very close to the tion obtainable at the critical point for exceedingly small adjustment of the compensators compensatory to Is necessary to start or stop oscillations after the second and third compensators compensatory are properly adjusted they are to be left alone and the circuits can be brought up to the critical point by manipulating the first compensator alone there Is an interesting point in con com lection with the placing of the feedback colla coils which deals with their position with respect to the darlea of the tuning units constructional the first step in assembling this receiver Is to procure the best beat of the necessary materials A 27 by 20 inch panel and a 7 by 24 inch baseboard are fastened together in the customary mai manner laer after the panel la Is drilled with the necessary holes boles the construction of the radio frequency transformers Is not a difficult one three bakelite or hard bard rubber tubes 2 inches in diameter and 0 inches long are required there are wound 45 turns of no 22 DOC wire A 6 turo tum winding of the same size wire composes a primary winding of an inch from the first winding the secondary winding Is then continued for another 45 turns the compensating coil to Is next placed on the tubing and consists of six turns of wire wound in the opposite 41 direction to that of the other windings two small brackets are used to fasten the radio frequency transformers to ae baseboard the above description pertains to two of the transformers the third being slightly different in that the compensating pen sating coil instead of being wound on the tube itself to Is placed on a small rotor at one end of the tube this rotor Is a piece of bakelite tubing two inches to III diameter and one inch tong long at one end of which Is placed the six fix turn winding it Is not necessary that the wire be wound in any spec specific iffe d direction since the coll coil can be readily turned through degrees and ahto change its ita polarity the wiring of the receiver la Is not very difficult since there are no set rules except that careful work brings good results in case trouble to la experienced perien ced from the begin beginning nini the connections to the compensating colls coll should be reversed one at a uwe time until the undesirable oscillations are eliminated it will be found advisable to place two bypass by pass condensers across 1 the he B battery and also to use a road mad condenser between the ar grid id and plate terminals of the last audio frequency cy amplifier tube As regards the selectivity of the set act it Is safe eafe to say any that it sur surpasses the tile majolly of those on abd tbd tb market today in III sensitivity too due fi 1 jie be exacting values of the appart apparatus alsed and the corrects correct 1 engin engineering liering principles involved v the receiver stands as aa a big step p in the development of tuned radio frequency sets eta As aa will be W noted the colls are tuny fully 0 6 inches apart reducing to a mint mom the tendency towards inter stage coupling with resultant oscillations of audio iu adl frequency amplification fi willbe found to give mor 11 thin f q 4 tt being nece eary to ahr incorporate a by paw con trad aud platt plate tw of abe 1 iia tob |