The A.C. Browning Drake

Radio Record, Volume III, Issue 12, 4 October 1929, Page 31

The A.C. Browning Drake

ae Coil Considerations ITH the multitude of possibilities of coil condenser combination for this set the full details for any one combination was not given in the original description. It was intended that the set would be made by constructors who have had a little experience in coil construction and who were in consequence able to work out the specifications of this for themselves. Some constructors who do not have any apparatus on hand and who in consequence have to purchase this will be advised to follow the following details: Obtain a piece of two-inch diameter cardboard formér about eight inches in length, a quarter pound of 24 d.s.¢. wire and a few yards of 30 d.s.c. Wind the aerial coil first. Drill two very small holes in the end of the former (marked G) and thread the end of the wire through this so as to make a substantial hold. From the lowest of these holes measuré two inches and drill another two holes (marked B). Measure 4% inch from here back toward the first hole and perforate the former to allow a loop of wire to be passed through (marked A). Commence winding. When the perforation is reached, bare the wire and pass it through as a loop, catching another piece of heavier wire in the loop inside the former. Tighten the wire and proceed until the last two holes are reached. Cut the wire and pass it through the holes. Water solder the joint to the loop. Leave sufficient to make a connection. Leave a space of an inch, and again drill two holes (marked G), measure 2+ inches and then another two holes (marked B-). from these two meastire back half an inch and make another slot (marked N). Commence winding, and proceed as before. The coils on completion should be aerial coil 78 turns tapped at the eighteenth, grid coil 87 turns tapped at the fifteenth. A smali variation from these specifications will be immaterial. Provision has now been made for tuning the aerial coil with a .0005 mfd. condenser and the regenaformer with a .00035 mfd. The connections are evident from the rest of the description. The more experienced may depart from these specifications, and where the coils are already in use in a Browning Drake merely transpose them to the new set, do not rewind them unless economy in the size of former is required. The tickler comprises about from 15 to 20 turns wound on a smaller former and pivoted under the. grid end of the grid coil by bolts, washérs and céllars. The ends should be fastened to flexible wire and brought across to the main former. The terminals should be marked T and P1, but the connections to them may have to be reversed on try-out, so it is not advisablé to solder them at this stage. | The description of the primary was | sufficiently detailed, so that further description this week is unnecessary. | One end goes to B-- and the other (P) | to the condenser 0.5. The connections | may have to be reversed later. :

"When commercial coils are used 2 few alterations are advisable. The promary should be removed and the turns reduced to 15 or 16 in the case of a two-inch former. Like other specifications, these alter for different conditions. Those who wish to make excursions into the realm of simple mathematics can use the following simple formula for determining number of primary turns :- T P = --_----- 200,000 Vv Ri where P = Number of primary turns. T = Number of turns on the grid coil, __ Ri = Valve impedance. Another alteration to commercial coils where neutralizing is carried out from, the end of the secondary is to discon nect terminal marked N, connecting it instead to the fifteenth turn. from the bottom. This loose end could with advantage be removed.