Basic step up dc-dc converter
This is a basic circuit of a step up DC-DC converter which the output voltage is more than the input, the circuit could be used to power a 9v or more devices from a 6v or even a 1.5v battery, charge batteries (3-12v) with 1.5v solar cell…
The circuit uses an oscillator using Schmitt trigger, all types of oscillators works, one transistor (Ex: BD139 or similar), resistors, coil (many different types of coils work even a small DC motor works! or you can wind 60 turn on ferrite)

R1 and C1 determine the oscillation frequency, different types of coils perform differently at  frequencies changes.
I used 5v input and toroid ferrite, the output exceed 60v (no load). The output voltage will drop as the load go higher.

Other types of oscillators can be used:

Other one to use see here: Simple rectangular oscillator

7812 or 7805 regulators can be used to stabilize the output voltage. (remember not to exceed the maximum input voltage)