TIPS AND JOTTINGS

Manawatu Times, Volume LIII, Issue 6541, 24 February 1928, Page 11

TIPS AND JOTTINGS

Many new listeners will be interested to hear that during tho currency of the Dunedin Exhibition of 1925-26, ■ the broadcast station, VLDN, at the i eluded. A capacity of .001 has no ef- ; Transmission was six nights a wook, chiefly of the Argyll and Sutherland Highlanders’ Band, which, unfortunately, seldom camo through as it j should have done from the outside bandstand. Items from the concert hall camo in at Wellington with good volume and quality, “Megohm” employing a five-valve T.A.T. circuit. The closing ceremony of tho exhibition took place in the afternoon, which was, sunny and bright in Wellington, and with tho circuit mentioned, tha writer, seated some distance from the loudspeaker, heard quite distinctly every word of tho valedictory speeches. A unit that will interest experimenters and others is known as the “Abox” Filter, now on tho American market. This permits those who have a good two-amporo or five-ampere chargor to convert it into an A eliminator. The Abox filter smoothes out the current from the chargor, and thus perfect A , elimination is obtained, sufficient to run six valves of the 201 A type, provided that the charger Will supply not less than two amps. The filaments remain wired in parallel in tho usual way. The life of valves and lamps is often quoted as being 1000 hours. This represents twelve months’ service fit tho rate of nearly 2'| hours every night. Tho object of the fixed condenser across the primary of the first audio transformer is to shunt to earth the radio frequency currents necessary to supply reaction, after they have passed through the detector plato circuit. Those R.P. currents nro earthed to-prevent them entering the audio side, from which all R.P. must be excluded. A capacity of .00- has no effect upon audio, frequencies of as high as 5000 cycles, and larger valves may often bo used without distortion occurring, but only if necessary to control tone. But in a resistance capacity coupled amplifier the by-pass condenser has quite a different effect, and must bo kept very small in capacity, say .000.1, in a circuit with moving tickler. If bowling occurs in a two-stage crystal amplifier, reversing the connections to tho primary of the second transformer will often effect a euro.

An American radio journal expresses the opinion that manufacturers have of lato devoted moro attention to decorating the loudspeaker than to improving its reproducing qualities. When working several salves off a B accumulator, to prevent unequal drain upon groups of cells supplying R.F. detector, and audio, the full battery voltago may bo taken and resistances inserted, in the common plate circuit of valves requiring less than tho maximum voltage. This moans dealing with the accumulator output in the same way as is dono with B eliminator voltage. In the explanation last week of how to check up B eliminator consumption on the meter, tho “hundreds” dial was mentioned, but this should have read “hundredths.”