Radio Broadcast (May 1928-Apr 1929)

OCTOBER, 1928 THE "VIVETONE 29" RECEIVER 367 5" VIEW OF END A • INDICATES HOLES ALREADY IN CHASSIS. O INDICATES ADDITIONAL HOLES TO BE DRILLED. THESE SHOULD BE 3/,| DIA. UNLESS OTHERWISE SPECIFIED. VIEW OF END B FRONT-, 3— if 1— ii— BEFORE DRILLING ANY NEW HOLES. MOUNT 4 BOX SHIELDS ON CHASSIS. THEN MARK PENCIL LINES ON CHASSIS AROUND INSIDE WALLS OF SHIELDS. REMOVE SHIELDS AND USE PENCIL LINES TO LOCATE POSITIONS OF NEW HOLES. -Irvi 3" : 4*1 -in~T" -ICM x "r:r j M DIA. | • I • r1; T X LI -BACK VIEW OF CHASSIS FIG. I. THE LAYOUT OF THE CHASSIS structor or custom set builder may choose the power supply unit that suits his pocketbook, or may pick out the one which gives the greatest amount of output power at audio frequencies. The quality of reproduction that is obtainable from the receiver with either of these units or with any good amplifier and power equipment is comparable with the best receivers on the market to-day. The tuning equipment illustrated and described here can be used, of course, with any amplifier. The output of the detector may easily be placed on an amplifier of any number of stages or of any type of coupling devices. With the advent of the newer power tubes, the constructor is advised to go in for the best he can afford, since a receiver made of the best apparatus now purchaseable should be able to stand up in comparison with the receivers to be designed and built for several years to come. In other words the best possible receiver and power equipment is, in the long run, the most economical. Unlike the automobile, it does not depreciate at a very rapid rate. The receiver is batteryless. It is entirely electrified with either of the power units the writer has built or with any power apparatus which operates from a light socket. This is accomplished by the use of 326 and 327 a.c. tubes. CONSTRUCTION pROBABLY the most ' novel part of the receiver so far as the home constructor is concerned, is that all the parts in it are standard and can be purchased at most dependable radio dealers. The sub-base and box shields are standard products of the Aluminum Company of America and most of the holes required for mounting the parts to this sub-base have been punched in during the manufacturing process. The few additional small holes required can easily be made with the aid of a small hand drill which is most generally part of the radio technician's tool kit. Fig. 1 shows exactly where to drill these holes. The construction of the receiver is simplicity itself, and is clearly shown in the schematic and picture wiring diagrams in Figs. 2, 3 and 4 and the panel layout in 1 ig. 1. Resistor PP-2000, whose variable arm is attached to the gang condenser shaft, is mounted on a brass bracket 2 Jg" high and f " wide screwed to the chassis. Each of the r. f. coils, 9072, is mounted by means of two round head machine screws 1 " long, being thus raised above the chassis. Fullsized drawings and additional constructional notes on the receiver and power unit number one and number two may be obtained from the writer. To cover the cost and postage they are priced at $1 .00. FIG. 2. THE SCHEMATIC DIAGRAM It will be noted that the circuit diagram calls for grid suppressors of 400, 500, and 600 ohms for the three radio-frequency amplifiers. Decreasing the -values of these resistances increases the amplification. For example, a good combination would be 300 ohms in the first stage, 400 in the second, and 500 ohms in the third. They may, however, be decreased to as low as 200, 300 and 300 for the three stages respectively. This, of course, is to be determined only by the one who is constructing the receiver, since some like to tune in stations without experiencing regeneration, while others like the "swish" of a slightly regerferative set as they go through a carrier signal. THE CABINET THE writer's receiver is housed in a Corbett cabinet 7" x 26" x 10" deep. The cabinet had to be prepared for its reception by cutting out holes for the cable plug and the antenna and ground connections. To have the chassis of the receiver fit snugly in the cabinet it was necessary to remove a small portion of the wood at both the front and back corners. These cabinets, however, may be secured from the Corbett people with such alterations already made. If the constructor is careful his efforts will be rewarded with a magnificent receiver. The set can be placed on a table or in one of the special cabinets which houses the power supply apparatus in the bottom. A model of this receiver has been in operation at the writer's laboratory for several months and its performance has given considerable satisfaction. The laboratory is located not over a half mile from B1-4 v Indicates connection to metal base