Tips and Jottings.

Radio Record, Volume II, Issue 12, 5 October 1928, Page 27

Tips and Jottings.

Artesian Well Earth. CARTERTON constructor says :-- "My earth is a pump bore 3dft. into sandstone. Needless to say it gives great results, and at between 5 o’clock and 7.30 my dials are a solid mass of Yankee stations. I have given up all hope of sorting them out." This is a good tip for any listener near an artesian well to connect an earth wire to the pipe and note the result. Aeroplane Radio Generators. N answer to a query, aeroplanes usually derive current for their radio transmitter from a small dynamo fitted with a propeller, which is driven by the air when the ’plane is under way. Thoroughly "Dud" Output Transformers. N American dealer gave a wholesale firm a trial order for two output transformers at a low price. When they arrived he attempted to measure . the resistance and found that the coils would pass one ampere at 85 volts! The cover was torn off and revealed two short coils of resistance wire connected from "in" to "out" on each side, consequently the inductance was practically nil. A block of pig-iron was included to give weight. Coil-Driven Loud-Speakers. AN American journal says: "We have already mentioned the superior qualities of the Magnavox and Jensen speakers. We have recently seen a curve which we believe to be truthful -which shows a uniform response from below 35 cycles to above 6000 when a unit of this type is used with 4 rather large and awkward baffleboard. We do not believe it necessary to go down to 35 cycles for excellent quality -hbut it is comfortable to know your automobile can go 75 miles an hour even though you haven’t the nerve to drive it at that rate. The trend toward dynamic speakers is already evidenced in the interest shown on Cordtlandt Street, the cutrate market of New York. Here are a half dozen imitations of the real thing. which the gullible radio public is buy ing as fast as it can. It is reported that several receiver manufacturers. whose names are well known, are interested in the dynamic speaker, and that several have already made arrangements for using it in 1929 models. B Eliminators not Suited for Short-Wave Reception. THE sensitiveness of the detector circuit of a short-wave _ receiver, which is invariably built on the "lowloss" plan, makes it extremely suscep-

tible to alterrating current variations of any kind, so that the slightest trace of ripple in plate current is made apparent. Even with a B battery in use, there is often trouble through the aerial or lead-in picking up a.c. hum from power lines or house-wiring, and this trouble is naturally far more pronounced when there is direct connection, or nearly so, between the receiver and the mains, per medium of an eliminator. On short-wave reception, too, the slight variation in plate current caused by line fiuctuation, makes it impossible to maintain critical adjustment. Aluminium Quality. In America, commercially pure aluminium sheet is designated as "28." An aluminium-manganese alloy sheet of lower conductivity is designated "38."