A POWERFUL AMPLIFIER

Radio Record, Volume I, Issue 42, 4 May 1928, Page 4

A POWERFUL AMPLIFIER

TEN LOUD SPEAKERS. HNTERTAIN LARGE CROWDS GN ; ANZAC DAY, | A interesting adaptation of radio apparatus to the amplilying of public addreses was demonstrated at the Wasin Reserve, Wellington, ou Anzac Day, by means of an imsiallation fitted up by Standard Cables and ‘Telephones, Lid. Ky means of this apparatus every word of the speakers was heard by the crowd of some thousands that was present. Ten loudspeakers fitted with ebonite horns, 3ft. 6in. in length were grouped ii four pairs at suitable parts of the ground, whilst the remaining two faced the grandstand. ‘I'wo microphones were used, one on each platforin, The actual amplifying system used igs designed to give an output of 15 to 20 watts to work the londspeakers, this beivg accomplished by jour stages of aniplitication employing cight valves in all. The first two stages consist of a single 5-watt vulve each, followed by a stage of two 5-watters in a pushpull stage, whilst the last stage consists of another push-pull with two 20watt valves on each side, or four valves. Current for the cight valves was all derived from accumulaters, 12 watts for the filaments, 350 volts for the plates, and about 50 volts grid-bias. It can well be imagined that the ontput from such an amplifier would be sufficient to give the required volume fiom a number of loudspeakers, which thereby enabled the whole crowd to hear the speeches instead of the hearing being confined to a limited few near the platforms. = 7