[GreenKeys] ring signal

[Joe Stevens]

They used everything imaginable and a bit more.  Generators turned by 
motors, mechanical vibrators, some devices like a dynamotor with 
motor and generator on one armature, and electronic multivibrators 
both tube and solid state.  Several frequencies were used with 20 Hz 
being most common.  For multi-party lines there were a couple of 
different sets of frequencies that rang resonant ringers in the 
subscriber's phones.  30 Hz, 42 Hz and 66 Hz ringers are in my junk 
box.  Frequencies as low as 16 Hz were used.  For key systems, 30 Hz 
was common as it was easy to divide the 60 Hz line frequency by 2 
with a ferroresonant transformer.  There are small Wescom ringing 
supplies out there that would be nice for a small home exchange (see 
ebay 200280976107).  30 Hz will ring almost any phone very nicely as 
most phones don't care much what frequency it is.  Many but not all 
of the power supplies for 1A2 key systems will provide 30 Hz ringing 
and most of the voltages one might want for a home phone system.  One 
is shown at the bottom of the cabinet in ebay item 120369441610 
.  For 48 volts just series two of them.

Much like the current limiting on a telegraph loop, the ringing 
voltage was current limited so if there was a fault on a subscriber 
line, there would be no fire started.  There is one story, however, 
about making a dog bark...  The voltage might be between 90 and 160 
volts AC with the higher frequencies being a slightly higher voltage.

For good recordings discussing this, see    www wideweb com / phonetrips

73,

     ...j0e   WL7AML

www kadiak org / tel




At 11:28 PM 2/10/2009, amourdutigre wrote:
>I was curious, how did the telco COs generate their ring signal? I 
>believe that it is a 20 Cycle AC current.
>
>Did they use dynamos or did they use an oscillator? I remember an 
>old phone tech that had a ring signal generator that was built on a 
>chassis and had tubes. That is about all that I remember of it. That 
>was in 1979.
>
>Thankyou in advance!
>
>73
>
>Joe KB0TXC
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