I have several ways of testing the ringers for phones, but one of the simplest I built several years back using a Black Magic LSN 12 - 86 module. There is also a 5 volt version, and a 24 volt version made.
These modules, available from http://www.camblab.com/
are great devices, in a potted case, .5" high x1.5" wide x1.5" long.
You will occasionally see these on eBay for a very good price. If I remember correctly, I bought two for $7 ea.
All that is needed to make a great portable ring generator, is the module, a small Radio Shack 3 .25" long x 2 " x 1.5" case, a momentary contact push-button, a 23A Cell Battery Holder, 23A 12 v battery, 330 ohm 1/8-1/4 watt resistor, a modular socket out of a cheap scrap phone, and a pair of terminal posts.
No need for a PCB - simply mount the module with double sided foam tape upside down in the case, and solder directly to the 4 pins.
Wiring is very simple. Neg. from the battery goes to the - terminal on the generator. Pos. from the battery goes via the momentary contact push-button to the positive terminal of the module.
One ~ output from the generator goes directly to the red lead of the modular socket (mounted below the posts), and to the red terminal post. The other goes from the other ~ terminal via the 330 ohm resistor (for short circuit protection - I forgot to mention this in my original post) to the green lead of the modular socket, then on to the remaining terminal post.
Plug in a modular phone, or use clip leads to the red and green wires from a non modular phone, press the button, and if the phone is wired for non-party lines, it will ring away!
Each 23A battery will last several months under average use.
This makes a great portable ring generator to test phone ringers and as an aid to wiring them correctly without connecting them to a phone line (no-one would test them out directly on a phone line, would they?
Most of the time, I use my much larger Radio Shack tester to set up phones, or test it on my 555 or switching demo, but this unit comes in very handy at times due to its small size and portability. It will produce up to 5 REN with 86 volts AC 30 cycle.
Just thought I would post this today, as I had it out changing the battery. It is a great adjunct to your toolbox, and indispensable if you don't have another ring generator!