Frequency Converter

I want to know if it is possible to make a frequency converter, using components like transistor, transformer, capacitor or any other simple discrete component...... I would like it to be able to vary a 12v AC between 75Hz and 35Hz or maybe even lower ...... I was thinking of oscillators but i don't know how, and I am yet to even grab properly the basic working principle of an oscillator....

I have found this forum one of the most helpful tool in my studies of electronics..... I am grateful for all answers that has been given, and I am also appreciating all replies on this new questions..

*BIG THANKS TO ALL*

Question:

1. You said "frequency converter". By 12VAC do you mean the input is intended to be 60Hz, and you want to convert this to a variable frequency (35-75Hz)? Why not just make it a variable frequency generator that is powered by the 12VAC source?
2. What kind of power does this need to deliver (i.e. what will it be driving -- if anything)?
3. Are we talking sine-wave output/input...or something else? And if sine-wave, how pure of a sine-wave (level of expectable distortion) on the output?