Useful Tips and Jottings

Radio Record, Volume II, Issue 34, 8 March 1929, Page 30

Useful Tips and Jottings

A Light Within. E grope within our cabinets when changing valves, when altering coils, or when making those necessary and critieal adjustments often called for-grope within cabinets which are non-illuminated. Valves are inserted or tried the wrong way round. TFilaments burn out. Coils are terrible devices to plug into socket holders which cannot be seen. And all this inconvenience can be obviated by lighting up the inside of the set with a 3-volt lamp which costs 6d., fitted to a holder which costs the same, and supplied with current from a battery worth 4d. The only other ingredient required is a switch which costs 3d., or which can be made with two old terminals and a hooked piece of wire. As this lamp is required on comparatively rare occasions, the battery lasts a long time. Only those who have thus equipped their sets know the value of an addition which, at least, saves many a bad temper and unparliamentary expressions. A.C. Hum. C. hum frequently occurs in @ ra"ceiver, even though the receiver itself is not connected to any accessories using A.C. power. This hum is often picked up by a lamp or conductor in the immediate vicinity of the receiver. Quite a common practice is to place a lamp on top of the set to illuminate the tuning controls. Naturally the lamp, and the lamp cord suplying the A.C. power to it, are in close proximity. to the instruments in the set, which, .due to their sensitive nature, pick up any interference generated in the field nround the conductors. It is best to investigate all lighting fixtures in the vicinity of the set in attempting to eliminate the hum. Tinning the Soldering Iron. The professional set builder finds that he spends a considerable amount of time keeping the soldering iron well tinned.. This can be overcome by keeping the tip of the iron partly submerged in solder in the following manner. Procure a block of wood about 10in. long, 4in. wide, and 4in. thick, upon which mount a heavy piece of transite board. To one end of the block fasten a can cover such as may be procured from a baking powder can. Then at at the other.end of the block

of wood a stand is mounted which may be constructed from a piece of heavy wire. Melt considerable solder in the can cover and place the tip of the iron in it. This keeps the iron from coming in contact with the air, and consequently keeps it free from oxide. Preventing Turning. ANOTHER way of ensuring that terminals do not turn in the panel when the receiver is finished is to fit them with locking pins. To fit the pin, put the terminal up-, side down in the vice. A block of ® wood underneath will help to support it and to prevent it from tilting sideways. In the underside of the head drill! a hole with a fine drill, midway between the shank and the edge of the head. In the hole put a piece of hard brass wire. This should be a tight fit in the hole, projecting about 1-8in. To mount, drill the usual clearance hole in the panel for the shank, put the terminal in, and give it a light tap with a mallet, so that the pin makes a mark on the panel. Centrepunch this mark, and drill a hole with the same drill as before. When you put in the terminal, tap it home with the mallet, and secure with the usual nut. Caleulating Accumulator Capacities, [THE actual capacity of an accu yf) lator can quickly be calculated ic the size and number of plates are known. If the case is celluloid the procedure is simple. The number of positive plates is counted. These can easily be distinguished by their brown colour, compared with the blue grey of the negative plates. The length and width of each plate is then measured. in inches. Calculate the capacity according to the formulae as follows :- Cequaus NXLXWXK. Where N equals number of plates. L. equals length of plates in inches. W equals width of plates in inches. K equals a constant (with commercially made plates this is Va 17). ra C equals capacity of accumulator in amps. When charging an accumulator the charging rate should not exceed onetenth of the actual ampre-hour capacity as determined above.