5v powered phone ring generator circuit
I once designed a circuit that replaced the old wind-up magneto generator in trackside telephones that was used at very remote railway level crossings. The phone, (when the button was pressed) basically rang a standard telephone bell many miles distant in a signalman's railway box. I believe that some may still be in use on some remote parts of the East Anglian railway network in the UK today. They were built to last and looked like this: -



The one above may have been a type with a DTMF auto-dialler but you wouldn't be able to tell the difference between an auto-dialler and an electro-magneto type. But, I digress. 

The circuit was powered by 4x D type batteries producing nominally 6 volts DC but, conceivably it will work at 5 volts or 4 volts etc. It used a 25 Hz sinewave oscillator (probably a square wave relaxation oscillator with some post filtering to make it nominally sine wave ish) that fed a stereo bridge amplifier capable of delivering a few watts of power. This was back in 1988 so forgive me if I forget the part number of the amp.

The bridge output from the amp fed the secondary of a standard 230/6V AC mains transformer and the output from the transformer (the 230V winding) nominally produced about 100 volt RMS. It was adjusted to this value by adjusting the amplitude of the sinewave fed to the bridge amplifier.

It worked beautifully and now all that remains, for anyone reading this post, is to fill in the gaps. Sorry I don't have a schematic but it's not rocket science!