Thread: REN Booster
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Old 27th Feb 2011, 1:07 pm   #22
russell_w_b
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Default Re: REN Booster

Quote:
Originally Posted by dagskarlsen View Post
A max at about 4 μF in the master socket.
The 3k3 resistors replaced by a 0,5-1 μF depending on ringer.
With your capacitor values, an assumed ideal voltage of 75V RMS at 25Hz at your premises and using typical type 59A bell-motors in your telephones, the current, per telephone bell, for 1, 2, 3 and 4 instruments would be 12.3mA, 9.8mA, 8.1mA and 7mA respectively. These values are not a million miles from the currents if a 3k3 resistor were to be used in each telephone (1,2,3,4 telephones each drawing 14.8mA, 10.7mA, 7.6mA and 5.7mA respectively).

So yes, it would work, and you might even obtain a more pleasant 'ting', as the resistive element of the circuit is limited to the wiring and the winding resistance (at a.c.) of the bell-bobbins. You could back warm in the knowledge that none of your precious ringing current was being dissipated as heat!

If no telephones were connected, you'd have a test-line impedance consisting of a 4uF cap inseries with the 470k resistor (I have neglected this resistor in all of my calculations), but I don't think that would be a problem. With four telephones connected, each with a 1uF cap in place of the 3k3 resistor in series with the type 59A bell and a 4uF master LJU capacitor, you'd see 2uF at the incoming line. With one, two and three telephones you'd see 0.8uF, 1.33ruF and 1.7uF respectively - I guess all would work.
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