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How to Build a Two-Stage Radio-Frequency Amplifier
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scriber lines, if marked on the front, would be visible and unsightly unless removed by a graining process. Some builders will wish to provide a grained surface on the front of the panel. Graining may be accomplished by rubbing the panel along its length, with a straight motion, with No. o emery cloth. This is continued until all the glossy marks on the panel have been removed. The graining process usually takes place after all the holes are drilled. The panel is then polished with an oiled cloth.
In drilling the holes it is well to drill all of them first, with a No. 28 drill and then enlarge to the required size with the correct size drill. This procedure affords a more accurately drilled panel than if all the holes were directly drilled with the required size drills in the beginning. By referring to the panel layout in Fig. 6A it will be observed which holes are to be countersunk. This layout should be thoroughly understood before actual construction is begun.
In a similar manner of layout, the binding post strips and brass mounting bus-bar strip are prepared and drilled. See Fig. 6 C, D, -E, and F.
WINDING THE COILS
THE type of coil used here is termed the diamond weave. To wind these coils it is necessary to have a cylindrical wooden form (a rolling pin of the required size will do) 2# inches in diameter. Around the circum
Radio Broadcast Photograph
A SYMMETRICAL PANEL ARRANGEMENT
The jack in the lo^er left is for plugging-in a loop. Vernier dials may be substituted for those shown
ference of this cylinder, at approximately \ inch intervals are driven brass or wooden pins T3^inch in diameter \\ inches long. The coil winding form is illustrated in the sketch Fig. A. No. 22 d.c.c. wire is used throughout the windings.
The antenna coupler has only a primary and secondary. The other two coil units have a
Parts required : „ n 1 cylinder 2^8dia. 1 wide 15 spokes l^'long ^dia
SHOWING FIRST THREE TURNS ON FORM
FIG. 7
A. is a coil form for winding the diamond weaves.
B, How the weave is produced. Under two, then
over two, is the rule
Shows the first three turns in their relative positions to the spokes in producing a successive overlap resulting in the diamond weave coil
double-wound primary, constituting the N-P coils, and a secondary (S), as illustrated in Fig. 5.
The weave of the coil is produced as outlined in Figs. 7B and 8A-B-C. The first three turn positions are illustrated and will serve to indicate the progressive overlap of each additional layer of the winding. Success in this winding is all in the start. The beginning of the wire, allowing for a six inch lead, is fastened at the pin 1. From there it is brought diagonally to 2. From around the outside of 2 and 3 it diagonally crosses to 4. Here it again goes around the outside of 4, and 5, and so on. It will be observed from this that the winding style is continued over two and under two spokes.
Due to the odd number of spokes, the successive layers progress or stagger themselves. This permits a winding which makes the position of each layer wound different from