| Show AIN AW ma ar is 0 wiring diagram of the Four tube Tuba receiver by K 10 HUMPHREY la in th aba now new york tork horald herald tribune the quality four as an its name 1 implies m was designed with the express purpose of having a receiver with a minimum number cumber of tubes which would give quality above nil all else however after extensive tests it was coq found that it also bad good distance getting ability even when used with a rather short antenna the DX ability of the set met Is due doe primarily to the fact that regeneration can be employed in the two stages of tuned radio fre quency nency i being under control fit at fill all times and throughout the wave band of the receiver two stages of tuned radio frequency are used a potentiometer ti ometer controlled crystal rectifier find and two stages of transformer coupled audio frequency keeping in mind that the receiver was designed es as a quality proposition it might bo be well to go into the question of where distortion occurs in the ordinary receiver and how it may be eliminated distortion sometimes occurs in the radio frequency end and in order to eliminate this possibility in this receiver the colls were carefully designed and a volume control by means of a potentiometer was installed etall cd distortion may very easily take place in the vacuum tube when used as a detector in order to eliminate this source of distortion a crystal rectifier Is used in place of the tube transformer coupling used aad transformer coupling on the audio tide side to Is by far the most efficient means of coupling the tubes together since the rest resistance stance coupled amplifiers have come on the market there has been a marked improvement in the tha audio fre quency transformers due to the competition and no reader may be in the least afraid to use the improved types in order to depart from t the he hone borne made appearance which a good anny of this type of receiver are prone to have the use of brackets and a com foj m OR off CRIP 2 F I 1 i pit rt rooan atlon details detail of the radio I frequency I 1 rans transformers formers position was used to support the tubes and transformers all of the wiring was concealed beneath this panel and the general appearance of the receiver Is thra of a well built factory product for those who wish to t build up the receiver according to their own ideas a circuit diagram Is given I 1 showing bowing the various constants used in the circuit however if 11 the reader Is desirous rous of standard parts other than those in the actual model it Is in well tv v obtain all the parts and lay them bout out before actually drilling the panel it will be noticed that the panel Is given as having dimensions of 8 inches this war wap chosen in order to fit dt in a certain style of cabinet which also provided room for the 13 batteries at the rear however a panel of the standard size that to la 7 by 22 may be used it if desired and it will be found that the apparatus will fit at to in equally well laying out the the Is in made from a piece piece of bakelite the thickness should not be less than ahr e sixteenths of an inch the dimensions given permit the he use rise f a cabinet only 6 inches depp lc I 1 may be made wider then than 6 5 inches if it Is desired due allowance being mabb for the dimensions of the cabinet the crystal detector la is mounted on top of the panel by means of two small email brass brackets after the apparatus 2 well asem bled on the and front panel the wiring of the receiver may be ba taken up no IS 18 round bus bar was used throughout as 85 it Is found easier to handle handl that than tho the wire with alth out any particular advantage in the extra copper A diagram of one of the cons colls to la given showing the connections the grid rid Is always connected to the terminal farthest away from the primary end and the ID B plus lead to Is connect ed to the corresponding terminal on the primary winding it will be noticed that there lis Is a center top tap on each one of the colls coils both on the primary and the secondary this Is provided so that variable coupling may be obtained the center tap Is not used in this circuit except in providing two different aerial tops taps the whole primary being used for or a short aerial and center tap being used tor for an extremely long aerial to in order to obtain the proper selectivity coll cali data the distance between the primary and secondary winding should be ono one sixteenth of an inch this method of winding cuts down the capacity coupling between the primary and secondary and Is used for that reason the small size of the colls coils naturally limits the extent of the magnetic field and permits closer spacing than with the larger diameter colls coils of the solenoid type the number of turns on the primary to Is 28 and the size of the th wire no 82 double silk covered cavend magnet wire the secondary consists of ab M turns of no 80 30 double silk covered magnet wire it will be lourid that the primary will take up about five six of an inch and the secondary about one inch the receiver tunes in much the camj manner as ag the ordinary tuned radio frequency set the three dials will register approximately the same and may be logged in the rei rel fular way the aerial coll coil may be thrown out a little by the use of various sized aerials but no not t enough to cause avy any difficulty tn in tuning the condensers are of the revised straight line variety and aid give plenty of spacing between all the stations from the lowest to the highest e s t the potentiometer gives an absolute control of regeneration in the radio frequency tubes and for local reception should be turned rather well hack back to the left for distant stations the receiver may be brought right up ti the point of oscillation and held t alre re it Is 1 nt at this point that the receiver to is most sensitive and most selective lec tive just a word about the serial aerial the average aerial of about eighty feet in length seems to give about the best beat allaround all around results though a longer aerial will tn in some lo locations catlone improve the distance list of parts the list of parts required and it Is to be recommended that the builder obtain all of the parts before a single thing ti is done tn in regard to the actual assembly of the receiver Is as follows on panel 1 by IS 22 by iia inches on one ert binet three thre 4 inch dials dial three ahr condensers cond nr and coll coils to rotten match one oil rheostat I 1 ohm one potentiometer one on single insl lck jack one on battery switch two supporting brackets bracket one on IS 25 bypass bap conden condonier con denier sir one on 1 I 1 con denter on microfarad fixed dired condenser two audio transformers transform fonner ere on air 10 by I 1 by 11 1 8 14 1 inches one on controlled crystal four sockets eight binding posts post wire spaghetti and d crows |
