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Testing A Ringer

Started by Lewes2, November 13, 2014, 01:00:01 PM

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Lewes2

I've learned since being a member of this forum that WE ringers are rated at about 90 volts of AC current. 

So, can one use an AC Variac, converting 120 volt wall current to 90 volts to test a WE ringer?  Or are there other factors about which I am ignorant that would prevent this from working? 

And what would happen if one connects a ringer directly to 120v wall current.  A pop, or smoke from burning coils? 

Uh . . . in any case, I would not be holding the ringer.  <g>

Chuck

Phonesrfun

House current in the US is 60 Hz (cycles per second).  A straight line ringer responds to  20 to 30 Hz, and would only emit a little bit of a 60 Hz buzz if run through a Variac.  120 volts from the house current would probably overheat it and might result in that poof of smoke.  I have never tried it that way, and wouldn't.


Other than connecting a ringer in a phone and calling the phone, you need to get a ringing current source.  These include such things as a magneto, a 115A frequency generator from a 1A2 key system, a small office PBX like a Panasonic 308 series or 616 series, or a solid state generator that are sometimes available on ebay.

Don't plug it into the wall. :)
-Bill G

Kenton K

I second. A magneto. They work great! Plus they are pretty cheap

Kk

Lewes2

A magneto?  You mean like an old hand crank phone box I see on eBay.  Or something else?  If something else, could you point me to an example. 

thanks. 

And I won't plug it into the wall.   :D

chuck

unbeldi

#4
The ringing signal of a telephone system typically has a frequency of 20 Hertz, or 30 Hz for key systems.  This is only one third (one half) of the frequency of utility power in the United States. European countries use a frequency of 50 Hz.

If you hook up a typical ringer to 60 Hz AC, you will find that they don't ring at all, because the resonance frequency, combined from the mechanical properties of the ringer and the electrical characteristics of the ringer circuitry, is close to the nominal ringing frequency.

See here for some measurements of the response curves of some common ringers in the Bell System:
http://www.classicrotaryphones.com/forum/index.php?topic=11948.msg126966#msg126966

It shows the impedance of three types of ringers as a function of frequency and also the response (loudness) of the ringer. You'll see that the standard types of Bell System ringers don't work at 60 Hz.

The resonance frequency of a ringer and its circuit is the frequency when its impedance is the lowest, meaning at this frequency it draws the most ringing current.

However, historically the independent telephone companies used ringing systems with a variety of frequencies other than 20 Hz.  This permitted them to ring one particular telephone of several on a party line.  Three major ringing systems were developed that used different frequency patterns or multiples.

I summarized these in another thread at one time:
http://www.classicrotaryphones.com/forum/index.php?topic=11938.msg126866#msg126866

There were however, ringing systems that did use utility power for ringing as well.  These were PBX systems in private installations.

The 90V is not actually design voltage for ringers.  It's a nominal value that was agreed upon in the industry, and the FCC specified a minimum as well, one half that value.

Turns out the historical frequency ringing system used voltages as high as over 200 V in the early days. Even in the 20 and 30s, the high frequency ringers required up to 160 V AC at ~66 Hz.  Kellogg was mainly responsible for developing more practical frequency ringing systems in the 1920, lowering the max. voltage to ~100 V for all frequencies.



unbeldi

The reason that many key telephone systems, like the 1A2, used 30 Hz ringing, instead of 20 Hz, was that 30 Hz AC is very easy to generate from 60 Hz utility power.  This can essentially be accomplished with one diode do eliminate one half of the sinusoidal wave shape.  However, this automatically generates an effective DC offset on the average, as the oscillations are not longer symmetrical about 0V, so one needs to filter the AC.  It also cuts the voltage in half, so a transformer is needed to bring the output to the appropriate value.
The response of the C-type ringers as found in the 500-series of telephones, extends just beyond 30 Hz without noticeable loss of volume.  However, they do sound a bit different, not as melodic, at 30 Hz.

Phonesrfun

Quote from: Lewes2 on November 13, 2014, 01:49:38 PM
A magneto?  You mean like an old hand crank phone box I see on eBay.  Or something else?  If something else, could you point me to an example. 

thanks. 

And I won't plug it into the wall.   :D

chuck

yes, the mag from an old crank phone.
-Bill G

dsk

If you have an old magneto telephone (e. a field telephone) this may be the easiest way to do testing.

This way you may use different speeds of turning, and the frequency will react on this.

A frequency converter (3 phase motor speed controller) may work too.

All the other converters are not that easy to get.

dsk