atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems WE 118A Ring Generator Circuit and components

Following up on this thread, I did just now find a circa 1961 "Bell System Record" document that describes the circuit of a 107-b frequency generator that describes generating 20cps ringing from 115 VAC/60Hz.

Skip to page 23 in this document:
https://telecomarchive.s3.us-east-2.amazonaws.com/docs/bsp-archive/BLR/39-7.pdf

..and find the article called "Static Frequency-Generators For Ringing Power". The term "static" in this context means "no moving parts", as would be the case with a motor-driving-a-generator approach to frequency shifting. This particular design appears to be a ferroresonant design (all passive components; transformers + caps) similar to the TelLabs 8101 schematic I posted earlier in this thread.

There does seem to be a path of revisions that lead to the very compact 118a 30Hz frequency generator (aka. ring generator) we're used to seeing in 551a/b/c shoebox KSUs. The procession I'm familiar with so far is: 107b -> ??? -> 113a -> 117a -> 118a. The latter three were "potted" in a block of plastic, the 107b was (apparently) just a couple of large donut-like wound wires in a partially open metal case with a lot of exposed wiring, presumably to let one configure different frequencies, due to the numerous transformer taps available. In the potted units, the frequency is "fixed" and not adjustable.

Here's pics of the various dedicated ring generators that I've been able to find so far; these pics from worthpoint's archive of previous ebay sales:

117a (30Hz):


113a (30Hz):


107b (20Hz):


I have myself a 118a and a 117a, and I /think/ I might have a 113a (can't remember). I can't find much other info on the 107b, such as if it is indeed "configurable" for different frequency outputs.