A Super-Regenerative Circuit

Radio Record, Volume I, Issue 43, 11 May 1928, Page 12

A Super-Regenerative Circuit

FOR LOOP OPERATION ONLY

[HIS type of circuit is particularly '" adapted for loop operation, being one that was awarded first prize in a "Radio News" constructional contest, for which it was entered as a two-valve portable set contained in a carrying-case 10 by 11 by 5 3-8 inches, loop, batteries and ‘phones being also contained in the case. This is not given as a tested circuit, but as one from which experimenters can get good results with a certain amount of patience. A great point about the circuit is that there is absolutely no hand-capacity, an unusual point in super-regenerative receivers. Although the description embodies points for portability, the circuit may be used effectively on a larger indoo: loop than would be employed in a portable set. THE ends of the loop aerial connect to the single tuning condenfer, C1, through the coil, L1; this

taning circuit being bridged across the grid of the detector tube, VI. The usual grid condenser and grid leak, C2 and R1, are used; the former has a capacity of .0001-mf. and the latter a resistance of 3: megohms. The tuning condenser is of the standard .0005-mf. size. The coils, L1 and L2, provide the regenerative effect, being connected in a regular series-tickler manner. Coil Li has an inductance value of 65 microhenries, and L% of 180 microhenries. Separate rheostats are used for the two tubes. The detector, V1, is a Philips valve, type B.406. Its filament is rated at 3.5 to 4 volts and 80 milliamperes, and requires a 15ohm rheostat. The low-frequency oscillator, V2, is a Vicco tube, with filament rating of 2.5 to 4 volts, .06 emperes; filament rheostat 30 oh:ns The "A" and "B" current is furnished by heavy-duty flashlight batteries contained in a compartment in the Set, case, as shown in the illustrations.

In the plate circuit of the detector tube is included the pair of headphones (each phone of 2,000 ohms resistance), shunted by a .002-mf, condenser. The ’phones’ themselves are shunted by a filtcring system, composed of the coil L3, of 100,000 microhenries, and the condenser C3, of .007-mf. From the grid-condenser connection of the detector tube a wire runs to the inductor, L5, in the grid circuit of the low-frequency oscillator, V2. -This coil is in inductive relation to another of identical size (L4, 180,000 microhenries) which is in the plate circuit. Each is bridged by a fixed condenser of .002-mf. Coil L4 obviously is a straight tickler coil, reacting on L5 to produce oscillations, the frequency of which is determined by the electrical dimensions of the coils and condensers. No filament switch is provided, nor ‘is one necessary. The tubes are

turned on and off by means of their individual. rheostats, which must be adusted carefully in order to make the tubes oscillate property. THE LOOP AERIAL. The loop aerial is of the flat variety, with one turn inside another on a simple X-shaped frame. The two ends of the cross bars that fit in the bottom edges of the cover are fastened by hinges to the latter, so that some adjustment of its position is possible. Od course, its directional effect is marked, and the set must be ‘Swung around so that the loop points. in the direction of the station to be received. The whole loop fits snugly inside the shallow top of the carrying case. INTERCHANGEABLE COILS. The tops of the case swings upward, the right side swings outward and the front folds down. The tuning condenser and the filament rheostat are mounted on a small panel, (Concluded at foot of next column). |

which forms the cover of a box containing the various fixed condensers and the coils L8, L4 and L5. Coils, L1 and L2, are not fixed permanently in place, but fit between clips on the right end of the instrument box. The earphones are not clamped in the usual U-shaped headband; instead, each is fitted with a half-moon clip which hangs over the ear and thus space is saved. As a guide to the number of turns on coils, 65 microhenries would represent, approximately, a coil of 36 turns, 24’s wire, and 180 microhenries, 56 similar turns. The equivalent of 180,000 microhenries would b- a 1,500-turn coil. construction and lower cost than those already given,