The Birmingham age-herald., 1922-10-22
THREE TUBE SET WITH ONLY TWO
 CONTROL DIALS
Super Regenerator With tho Minimum Number of Parts Produced After Much
 Experimentation
Bx JACK BINNS

After several weeks of experimsa.
 tai work we have been successful h
 producing a super regenerativs Fe-
 ceiver with two controls only. The set is the one recommended by Maj.
 E. H. Armstrong as the circuit best
 suited for the reception of music ana
 speech and employs two vacuum tubes for super-regeneration. and an
 additional tube for io-freQusnee
 amplification.
 The complete set stands on bass-
 board of bakelte, measuring 1t
 inches in length, IA inches in width
 and inches high. The wiring 10 entirely concealed beneath the base
 board, which stands on a wooden mount. A small bakelite panel
 seven inches high is mounted on the
 front to take the two controlling
 dials.
 In designing the set the purpose in view was to make as many of the parts fixed in value as possible and to eliminate all unnecessary appara- 1 tus. This Is entirely practical bat . slight exception is necessary, as VIII be explained.
 RheOstats Unnecessary He liESl tHIiB tEdl SHOulu Dc membered in the uper-regenerative
 system is that the first two vacuum tubes are required to be in the os- cillating state all of the time and consequently the filaments should be full on, Under these circumstances
 the filament rheostats are not neces-
 ssry and have been eliminated oom-
 pletely.
 To understand the reason why the | II haa oh Il haaf { s,t1f 1f,t state, it is necessary to explain their functioning. The second tube pro- duces oscillations at a certain deft- nite frequency which is determined by the two large duo-lateral coils in its grid and plate circuit. as well as by the condensers about the coils. The first tube acts as the regens- rative amrlifier of the weak currents that are picked up by the loop aerial, As 1t is really in the oscillating state With the filament fully turned on, 1t could not under normal circumstance function without distortion. As a mat ter of fact. however, 1t Is only Tn . theoretical state of oscillation, be- cause the lower frequency produced by the second tube is impressed upon l 1t, and counteracts the real effect of oscillation. In other words the second l tube acts as an automatic switch. ut
  l tube at sufficient number of times 1 per second to prevent 1t from pro | ducing sustained oscillations. In this manner the full simplifying possibili- ties of the tube are realized. l Switches Also Eliminated The next step that was underesileA was to determine whether it was pos 1 sfble to eliminate the switches and switch points on the primary of the | i ly satisfactory.
 l fourinch tube with seventy turns of No. 24 sflk-covered copper wire. All l of these turns are in the circuit. inin I ed in parallel with the loop. The rotor ] Is wound on a tube three and a half | inches in diameter with seventy-five turns of No. 30 enamel covered wire. i The dial connected to the rotor gives control of regeneration.
 | Only one variable condenser is used 1 in the circuit and this is shunted across the loop in order to tune for wave length. It is of the conven- 1 tional 23-plate type, with vernier l attachment for close tuning. | The remaining parts are all fixed, l and follow in detail the diagram pub l lished in this paper last July. There i Is, however, one exception. Wherever i a condenser is in the circuit the ia miliar micadons were used. These are little fixed condensers of various ca i pacities. which have two eyelets for connections.
 Condensers Mounted on Screws ] It was found that they were very 1 convenient for fixing the capacity 1 in the circuit, and thus eliminating the larger air condensers. The man
 ner in which they were assembled was as follows: Two screws with nuts were fixed on the bakelite base board in such way that the micadons could be slipped ever them, and then
 screwed down tightly with the nuts 1 In this manner it was possible to add capacity by putting more mica 1 dons on, or reduce capacity by re- moving them.
 i The constants for the condensers in | the experimental set were as follows: i Across the 1.25o turn coil, .0o25 mid, capacity; between the 400 turn and | 1.5o0 turn duo-lateral coils, .00O5 mid. capacity; between the 1,5o0 turn coil i and the common lead of the circuit. | .0o5 mid: in series with the choke coil of the filter circuit, .00l mid. l It will be found that the condenser between the 400 and 1,500 turn coils will have to be varied in it's capacity | to meet the characteristics of the particular tube used in the second socket. It is for this reason that hard and fast capacity cannot be given.