all oscilator are nothing but DC to AC converters ( in this aspect, this view is acceptable).......
based on the shape of the AC waveform u can select the type of oscillator .... eg., astable multivibrator for pulse waveform , hartly or rc phaseshift oscilltor for sine wave ......
You can build a sinewave generator, some examples you can find here: **broken link removed** https://www.epanorama.net/links/oscillator.html#sinewave
and then using an audio amplifier amplify this signal to 12Vrms (16.8Vpp) ..
Some amplifiers will give you amps of current at 12Vrms ..