Radio doings (Dec 1930-Jun1932)

December, 1930 RADIO DOINGS Page Forty-three FOR THE SERVICE MAN Automatic Voltage Control Perhaps the most important improvement ever added to the radio receiver to make it truly modern, is the automatic line voltage control. It has been proved conclusively that under'voltage causes fading, diminished volume, loss of power and sensitivity and generally poor reception, whereas over-voltage results in tube burn-outs, tone distortion and blasting, power pack break-downs, tube noises and lack of selectivity. In order for the set to operate properly, the a.c. line voltage should be maintained within 5 volts plus or minus of the rated voltage. This is exactly the range maintained automatically by the Amperite line voltage regulator, irrespective of the variations of line voltage. Amperite can be installed readily in any standard radio receiver. To in stall, it is simply necessary to cut one lead of the power supply line or cable at any place between the set and the house socket plug. The two cut ends are connected to the terminals of an Amperite adapter socket, or else an ordinary UXtype socket may be used, making connections to two opposite terminals and leaving the remaining terminals blank. The adapter or socket may be mounted at any convenient point, as shown. It is then merely necessary to insert the proper Amperite line voltage control tube and the receiver is ready for operation. * * * Improving High Frequency Response In certain commercial receivers, the response to higher audio frequencies is noticeably deficient. Especially in pushpull arrangements, this defect may be remedied by means of a simple expedient, involving the addition of only two extra midget variable condensers. These are connected as illustrated. Many interesting effects are obtainable by varying the settings of the two condensers. Care should be observed in handling the condensers to avoid the possibility of receiv IMPROVING RESPONSE TO HIGHER EREQU E N CIE5 \H P US H PULL AMP LI FIERS ing a shock from the high plate voltage. The principle involved in the improvement of the response range consists of nullifying the internal capacities of the tubes, thus increasing the response to higher audio frequencies. The improved results are well worth while, and give support to the contention that the use of neutralizing a.f. amplifiers has not been given the consideration it deserves. Parts Required — Two Silver-Marshall Midget Condensers, type 340 (1,2). Antenna and Ground Requirements All radio dealers and service men should be familiar with the latest wiring requirements of the National Electrical Code pertaining to radio receiver installations. The antenna wire must not be less than No. 14. The lead-in from antenna to building must also be not less than No. 14 if of copper, and not less than No. 17 if copper-clad steel. The lead-in conductor from the point where it enters the building to the set must have rubber-covered insulation. A lead-in strip, if used, must have approved insulation. Ground wire must be not smaller than No. 14 copper wire. Additional provisions are as follows: Antennas outside of buildings must be kept well away from all light or power circuits of more than 600 volts and trom railway, trolley or feeder wires so as to avoid possibility of accidental contact. When placed in proximity to light or power wires of less than 600 volts or signal wires, antenna must be constructed and installed durably and located with enough clearance to prevent contact with such wires cither by sagging or swinging. Splices and joints in the antenna span must be soldered, unless approved splicing device is used. Light socket antenna, if used, must be an approved device. Lead-in Conductors from the antenna to the first building attachment shall conform to the requirements for similarly located antennas. Lead-in conductors from the first building attachment to the building entrance shall be installed and kept so that they cannot swing closer to open supply conductors than 2 feet in case supply wires carry voltages up to 600 volts, or 10 feet where supply wires carry over 600 volts. Where all conductors involved are supported so as to insure a permanent separation and supply wires do not exceed 150 volts to ground, clearance may be reduced to not less than 4 inches. Lightning Arrester must be properly connected, if outside of building as near as possible to point of entrance — if inside building at some point between entrance and set which is convenient to a ground. Must not be placed in vicinity of ignitable stuff or exposed to inflammable gases or dust or flyings of combustible materials. Fuses, if used, must not be placed in the circuit from the antenna through the arrester to the ground. Ground Connector may be made to a cold water pipe where this is available, is in service and is connected to the street mains. Ground connection may be made to a galvanized iron pipe or rod driven into permanently damp earth. Gas piping must not be used for the ground. Grounding conductor may be run either inside or outside of building. If inside, wires shall be secured in a workmanlike manner and must not come nearer than 2 inches to an electric light or power wire not in conduit, unless separated by a continuous, firmly fixed non-conductor, such as porcelain tubes or flexible tubing. Storage battery circuits having more than 20 amperehours' capacity must be protected by a fuse or circuit breaker rated at not more than 1 5 amperes. "B" storage battery circuits must be properly protected by a fuse or circuit breaker rated at not more than 1 ampere in the negative lead. Fuses or circuit breakers shall be located not more than 18 inches along the wire from the battery terminal.