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Old 3rd Oct 2018, 11:19 pm   #10
russell_w_b
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Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
Default Re: British Telecom C2 klaxon and control box

Quote:
Originally Posted by 60 oldjohn View Post
We have a very loud klaxon here that is powered by only the phone line.
Bedlam Tonecaller? Made by Hosiden Besson? They use a rocking armature receiver and exploit the resonant frequency of operation by driving it at this frequency into a little exponential horn. They're bloomin' loud! Try putting together a rocking armature receiver, and 9V battery and a 555 oscillator around 1.5kHz with the receiver pointing downwards onto a hard surface with about a 1cm gap between and hear the difference it makes.

Re: the klaxon thing... When I was at British Steel in the '70s some of the PAX extensions in noisy environments were fitted with dark green ironclad relay boxes manufactured by the A.T.M. Company, which contained a similar relay, and would drive either a mains hooter or operate a light in sympathy with the ringing cadence.

The GPO Klaxon units I have seen - outside only - are mounted in a larger rectangular iron box which presumably has a physical barrier dividing the mains equipment relay contacts from the telephone ringing voltage.
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