Tips and Jottings

Radio Record, Volume V, Issue 33, 26 February 1932, Unnumbered Page

Tips and Jottings

for the Constructor

Shorts in Old A.C. ‘Sets. [S the older a.c. receivers the insulated leads from .the power unit were often pressed tightly. together under the chassis. | The rubbef insulation on these wires hardens and cracks with. age, causing short circuits; Trouble originating from.this source often is attributed to shorted condensers in error, eit! Ps . Trouble Light for;Battery Sets N ordinary panel light and socket may be permanently :mounted. inside the cabinet at any Conyenient point where i, will be found quite handy when it becomes tiecéssary to change valves or look for trouble. Leads may be run from the A battery binding posts and a small switch placed in one side of the line, or flexible leads terminating in small spring clips will do. Locating Trouble in Push-Pull Amplifier. : WHERE two type-245 valves are used in push-pull and one shows a blue glow, that valve may be defective, or overloaded because the other yalve is defective. Both valy#s should be tested to determine which valve should be replaced. Red Pencil Prevents Wiring Errors. HEN wiring a new circuit it is a good idea to have a red. pencil handy and draw a line over each con‘nection in the blue-print -as you complete the corresponding lead in the set. In this way a constant, check may be ‘kept on the amount. of. Work :completed, and no connections will ‘be overlooked. By adopting this scheme, néedless checking is avoided jas weéll-as loss through damage to valves ‘and parts. ; Fae . Drilling Bakelite... ‘pRILLS dull quickly "when -used on bakelite and similar’ materials, but their cutting edge will last much longer if the end of the drill is run through a cake of soap at intervals, Lutricated in this way the work is not. spoiled, ‘but the drill cuts a clean polished hole through the material. A flat piece of ‘hardwood. should be placed under the bakelite panel while drilling so that the hole will have a clean edge on the underside. , An Aid in Soldering Small Parts. JV HEN two small parts are to be soldered together, it frequent!y happens that, while heating one part, a previously soldered joint becomes sufficiently heated to come loose. Over:

heating may be controlled by. using a thin sheet of copper upon which ' to lay the work. Sheet aluminium is also suitable for the purpose. A sheet of metal, about 1ft. square, should be eimployed,- and. a hole is drilied in-one corner for hanging the sheet on.a nail w hen it is not'in use. ~ How to Strip Insulation From Wire. THEN building small coils, or wiring a circuit.in busbar fashion, the experimenter sometimes. requires a length of bare wire. If this is not at hand, it may be prepared by stripping the cotton. insulation from the proper‘size wire. To remore the insulation quickly, fasten one end of the wire to a nail and rub the insulation with a strip of medium sandpaper. Heavier wire, covered with rubber or fabric insulation, may be rolled into a coil and placed in a fire, and. after the insulation has been burned off the wire is brightened with sandpaper.

Removing Film from Antentia Insulators. WITHIN a few months’ time antenna insulators will gather a film of soot that will lower their efficiency. This is true of any type of insulator, and the lowered insulating value is quickly noticed in amateur transmitting installations. The effect in standard broadcast receivers is noted by the increasing difficulty in tuning in distant stations. It is a good plan to lower the antenna at least once every six months and wash the insulators with warm water or carbon tetrachloride, after which they should be polished with a soft rag. At this time. the antenna should be inspected for bad connections. and. the guy wires and lead-in checked. Adjusting Screws. SOME screws in a receiver do not,need to be permanently locked in.. position: in fact. they should work: éasily in their threads, and it is worth while giving such screws a dressing of lubricant before screwing them in. Screwadjusted components, for example, will work much more sweetly if you put a little graphite on the thread. If you cannot obtain the graphite as such, grind up the lead of a very soft (BBB) pencil finely. Add the smallest spot of thin oil. just enough to bind the particles together into a paste. Smear a very little of this paste on the thread of any screw, in wood, ebonite or metal, which you may wish to use in operating or to remoye again later. You can then he certain that it will not stick firmly in position. The lubricant will also save wear on fragile

threads, such as: those cut. in eboniie or bakélite.. Security, when you wish your bolts dnd nuts. to remain, firm indefinitely, can be ensured by, the application of shellac varnish ‘ after ‘tightening. up. Apply the varnish with a brush over both: bolt ‘and nut after assembling, warming the metal if possible to make the yarnish-run into the threads more readily. "Do not touch the varnish until it has set hard. If you should need to release the nut at any time, warm it first with a hot soldering iron, when the yarnish. will soften. Methylated spirit dabbed cn with a brush will have a similar effect, if the nut is inaccessible for the ‘hot iron, o Machining Aluminium Radio Panels. PLEASING machine finish can‘ ‘be given to aluminium radio panels with a round piece of wood and a drill. A piece of broom handle or dowel stock, about 3in. long, may ba used. A large nail, with the head ¢%t off so that it will fit the drill chuck, is driven into the centre at one end and. a piece of fine emery paper is fastened to the other, where it is held by a rubber. band. A hand drill can’ be used,. but a small electric drill is preferable. The panel is placed on a flat table and clamped down. The emery-covered end. of the tool is brought firmly against it and spun rapidly, thus removing the shiny aluminium surface in a circle as large as the end of the stick. The process ‘is repeated until the entire panel is covered with these overlapping circles.