| Show L eil J 1 y A Ar 9 r I o o c-o I ON The Revised Hu Hac CIrcuit In reviewing the long Ions line of or circuits circuit Which JI have e forged to 10 the front from In rC- rC re recent cent mouths months ench each one cine with It its Its Its- own special attributes claiming their due litH r amount of ot attention one cannot n no- no nes- nes 1 lest ct considering the lie very nr po la Roberts Built up around the older famous Roberts erts reflex It won Immediate approval ol and In Itt its present form Is satisfying Ilg its count count I Jes less users Yet when one looks over O I this circuit just as ns with others thero theIs Is 19 the constant urge fur I revision modification and sll slight hl II- II a 11 to make It better The Broadcast Magazine l laboratory In ex- ex experimenting ex experimenting with the version of or the orl original noh Ils I circuits line has tried out numerous changes with the he Idea Ilca of Improving ln i ithe the circuit Some of ot the changes mere mere- mt merely merely r I ly Jy consisted In replacing the dials with I those of a vernier type t pe while other changes were made In the actual cir clr circuit cult arrangement According to John Jolin n B Brennan tech technical editor of ot Radio Broadcast who describes the changes In a recent Is- Is Is eue sae of that magazine It was found that the substitution of a different form of ot regeneration In the detector circuit In place of ot the variable tickler method would permit smoother con con- control control control It would also eliminate the changing field set up by br the variation ot of tho the tickler coil coll position The meth meth- method meth- meth method method od found to be most successful and In- In In Involving Tolving the least number of changes wa was the feedback condenser regeneration regeneration regeneration tion tion system Involving only the addi addi- addition addition condenser tion of ot n a small variable condenser of the midget t type Tle and a 0 radio y choke coll coil Removing the Parts Part Parts In making this change the entire detector coil coll unit Is from Its connecting lends leads and removed remo-ed from the panel Then the tickler coil coll and ond Its shaft are remo-e remo removed by simply cutting cut cut- cuttin cutting tin ting off oIT that part of ot the strIp which supports the shaft and Its bearing bear bear- bearIng bearing ing The bushing located d on the top of the mounting strip Is re removed re- re removed removed moved from tho cut off section on and by means of ot a 32 0 machine screw Is fastened at the bottom of the mount mount- mountIng mounting mounting ing strip This Tills screw replaces the theone theone theone one used to hold the coil coll between Its Insulated support strips strips Now at ot that end of ot the secondary coil coll at ot which the coil coll Is located a tap Is made 13 turns from the bottom turn This tap may be Just below the letter Jetter S which Indicates the lie secondary of ot detector coil coll on the tho accompanying Ing diagram The detector coil coll may now be bo laid aside A plate 15 Hammarlund midget condenser Is mounted In the th hole for formerly for for- formerly formerly merly taken up by the shaft of ot the tickler coil coll When this Is accomplished accomplished the detector coIl coll mounting holes arc are spotted on the main panel These holes are ore drilled and counter counter- countersunk countersunk counter Blink sunk for the 32 0 machine screws which screw Into the mounting bush bush- bushIngs bushIngs bushings ings on the coIl coll unit To obtain regeneration satisfactorily with these alterations It Is necessary to Include a choke coll coil In the tho audio audio- transformer audio transformer primary circuit The choke Is employed to keep the radio radio- frequency currents out of ot the trans trans- transformer transformer former primary circuit so that the only path poth for tor these currents to take Is through the capacity element em em- employed employed for regeneration This choke coil colI may be mounted on the sub sub sub In the place left Jett vacant by discarding one of the parallel stage audio sock sock- sockets sockets sockets ets as Is explained later It will be noted the bypass condenser em- em em employed plo to shunt the primary audIo audIo- transformer audio transformer has been eliminated from the circuit At Reduced Volume Many times It Is found advisable to operate the receiver at ot reduced vol- vol volume volume vol volume ume In its lla Ilg original state the only away way to accomplish this was to Increase the value of resistance In the filament circuit of ot the tho radio frequency amplifier amplifier fier tier tube or loosen up on the regen regen- regeneration regeneration rallon or sensItivity control Quality sometimes suffered when the former method was employed Selectivity and ond sensitivity suffered ButTered In the latter As Asa Asa A Aft a ft final refinement for volume adjust adjust- adjustment adjustment ment and also as a tone control the rheostat and the fixed resistance tor for the frequency radIo frequency amplifier stage are aro removed remo In the audio amplifier cir cir- circuit cir circuit cult their volume control functions are taken over o by employing a variable high resistance resistance-Of of the value of ohm In n shunt across the secondary ot of the first transformer audio audio transformer One ot of the objects of ot this shunt resistance lies In Its tendency to give he the time amplifier fier tier a flatter characteristic that Is nil all frequencies will be amplified alike To make It possible to change readily from the last audio stage to the first audio stage required nothing more than Inclusion of ot a jack In the primary circuit of ot the first stage trans audio former At the same samo time It was found desirable to have some auto auto- n nf nt off the last lut I Jt r filament when the phones w were re 1 I d 1 don 1 on the lie first stage ut circuit l jacks dill did the trick To I employ this t type le of ur In the shown sometimes n necessitates e tes being made nailE to the jacks I however howe In III the lie circuit de described de- de deI I scribed in the Radio Maga- Maga Magazine Maga aga zine two No Xo Carter jacks were WIl taken apart and the blades re- re rearranged re rearranged arranged so o as os to correspond with the binds positions as ns shown hown In the nc- nc acen ac en m i circuit Ii I rn n-rn m As II a circuit Mr Ir Brennan rec- rec rec 11 II II 1111 limit ww use of ut the parallel tulle tube sockets In the lie last audio stage be re- re redness re removed moved MII mid amid Its wire wired In III the circuit to the radio frequency stage tac Then In the remaining last stage e socket n UX or UX tube Is employed as a power ver stage It will willbe be lie found toun that the shunt plate grid con con- condenser conI condenser condenser I denser for tor the llio last stage may moy be lie re removed re- re removed removed moved when the power tubo tube Is em- em emi employed em employed i 1 |
