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In the valve era, Bland Radio Pty Ltd of Edwardstown in South Australia made a centralized PA system for schools in Australia.
Contents
The central unit consisted of a preamp for a microphone, turntable, AM radio tuner, and a push-pull amplifier, and switches that would switch it to drive speakers located in the classrooms, and out in the school yard.
The speakers in the class rooms were a wedge type cabinet design, and were mounted on the wall up high, containing a 20 cm Rola loudspeaker. The "yard" speaker was also a 20 cm Rola, but housed in a large steel horn, that was mounted high up on either the wall of a 2 story school building, or sometimes on the roof of a school building.
The amplifier delivered a 100 volt line type output that coupled to the speakers via 500 ohm matching transformers, mounted in the speaker Enclosures at each locality.
Its Use
Usually this system would be used with the ABC's radio programmes for schools. The teachers would tune the tuner into the programme, and switch it to the appropriate class room or class rooms. This would sometimes also be done, for assemblies outside where the yard speaker would be switched in.
Other Improvization
Schools that did not have such a system, often played a tape, to get the children to march into assembly or set up a radio in the class room and tuned into the "for schools" programmes. The television was also used, and parents would donate old monochorme TV sets to the school, and they would be stationed in most class rooms, where they would tune into the ABC TV For Schools programmes. The TV set would be repaired if it needed a new valve, but not picture tube replacement.