Supplies 110v-30CPS ring power and an array of other voltages (including the ubiquitous 18vAC) in compact wall mount. Uses main transformer, then 'secret' potted module that has shape of a toroidal transformer + Electrolytic caps to cleverly halve mains frequency for ring. AC supplied through standard (for the time) Hubbell 'Twist-Lock' receptacle. Estimated vintage early 60s as CPS is used not Hertz.

Will come in handy for testing vintage phones.

Will come in handy for testing vintage phones.

Indeed, but should there be a photo or a link?

When photos are intended it is best to say "Photos coming" or similar.

Nice find. Where did you find it?

Is there a part number on that board? I can't see because of the reflection from the flash.

It's a model 20A -2 , Found Tech Bulletin (link) - dated 1978.
Don't know how it generates 30hz but they say it may be incompatible with Exchange 20hz

http://doc.telephonecollectors.info/dm/167-440-201_I6.pdf.

Thanks for the technical info.

What I meant was where did you find the hardware itself? I figure that's got to be a pretty rare item these days.

Don't remember where this one originated but they can be had from old buildings' line termination rooms etc.
I see it has Mfg date of Aug '66 on it. Plugged it in and looked at its 30cps on CRO (pic posted) looked a bit rough but it rings an even older "Film Noir" era (WE-300) phone nicely (2nd pic)

30 cps (clangs per second ) doesn't sound too bad but 25 cps (Aus) and 20 (US) sounds better - some 'Trimline' type phones with single gong seem to ring at half rate - 10cps - for very cool sound

I wonder if they chose 30 cps to differentiate internal PBX calls from external ones, as is often done with modern PBXs.

Seems you also like to collect solder.

"I wonder if they chose 30 cps to differentiate internal PBX calls from external ones, as is often done with modern PBXs."

I don't think so because the average person wouldn't know the difference but they could tell between, say, 25 and 50 (Aus) which some PBX's use for simplicity & economy? I think in US, AT&T used 30 in PBX because it's easier to derive from AC-60.

Which raises the question: How did exchanges traditionally generate 20/25? - I suspect they used a synchronous GeneMotor (back when electricity and maintenance staff were cheap!)

All right, I'm having 2nd thoughts now about 20/30cps:
You can actually distinguish, and it helped staff determine if call was internal or external. This was an added bonus of the simplified generation of ringing frequency outside of Exchange - given 1960s technology (an electronic inverter being too expensive & unreliable at that time?)

How did exchanges traditionally generate 20/25?

In Strowger /step-by-step exchanges they used one of these big mothers. It ran on exchange battery and generated the various tones and AC ring current. The cadences of the various tones are controlled by the cams you see at the front of the screen:

http://www.youtube.com/watch?v=VzIXvO6RahQ&list=PLgNzI09bRXtlv9-M7mrABEALyhplLpd-G&index=39.

Ahhhh they were the days - when a dial tone sounded like someone at the exchange was dropping their guts down the line.

Big generator has crane lifting hook on top! They add timing cams to gears (might as well).

2nd thoughts on ring frequency:
Low gong would sound on one half cycle & high gong on other half cycle, so 25 cps becomes 50? Thus the reason for lowered source frequency? And would be 20/25 on single bell phones like Ericofon® or Trimline®? Unless full-wave rectifier employed doubling pulsating frequency?

In Australia generating the ring voltage for telephone exchange or system was done in a number of ways. The early manual switchboards prior to 1914 used a version of a relay vibrator called a pole-changer but later used gas (i.e.coal gas not petrol) powered motor generators. Later again in the larger exchanges used a 50V genset like that mentioned by GTC. Smaller exchanges that had a reliable 240V 50Hz AC power supply used a sub-cycle ringing converter that was a tuned oscillating transformer that gave a 90V output at one third of the input frequency. These were designed and made in the USA with a 60Hz mains and would have had a 20Hz output there. However out here one third of 50Hz was 16 2/3Hz which just happened to work very well with the old style bell motors. In the 1950s there was an Australian made version that had a 240V AC input through a diode to deliver 50 half cycles to the transformer which was tuned to resonate at 25Hz. From the 1930s into the 1970s versions of vibrator and ringing converters were installed with PAX and PABX but are now hard to find in safe/operating condition.

From the description given by NewVista I think the WE unit uses the 'diode in the supply plus tuned transformer' method to halve the supply frequency hence a 30Hz output. It would also explain the incompatibility with 20Hz. I note from the scanned doco that the maximum input is 127V so it would not cope with an Australian 230V mains.

For Australian readers there is a small PABX ring generator unit available from Spence Electronics. It uses a 27-48V DC input and has a 25HZ output. (Note there is a typo in the associated doco that says 45HZ!). I have one and it works very well. If interested see:

http://www.spence-electronics.com.au/telecommunications/ring_generator.html.

Andrew