This 6V to 12V voltage converter circuit is made with an IC from SGS with several additional components. The IC is a TDA2003 but it can be replaced with a TDA2002. The cost of building the 6volts to 12 volts converter should be low enough to justify constructing it instead of modifying the entire equipment setup to work directly with a 6 volts power supply. The two principles of simplicity and functions properly without the need of the transformer.
The IC1 opam functions as a stable power multivibrator. Its oscillation frequency is determined by C3. Its oscillates at around 4kHz at standby and increases in a loaded condition up to around 7kHz. The output of the IC2 opamp is identical to the IC1 oscillator signal but in the opposite phase.
When the output of IC1 is at zero, the C4 charges via the diode D1 up to the power supply level minus the voltage drop at D1. When the IC1 swings to the opposite direction, its output become positive. The output voltage from IC1 adds up to the voltage stored at C4 forcing the diode D1 to stop conducting. C5 then charges via the diode D2 to a voltage that is double than the power supply level.
The theoritical output could reach the triple of the supply voltage. TO guard against unnecessary voltage increases at low current consumptions, a limiter stage was added to the circuit composed of a 15 volt zener diode and a darlington transistor T1/T2. This stage caps the output voltage to about 14.2 volts. To fiter out ripple from the output, C8 was also added. This helps prevent the hum signal from being noticed on radio or audio devices.
In constructing the 6 to 12 volts converter, attach the ICs to a common heatsink close to the pcb. The transistor must be attached to a separate heatsink. To get a much higher current output from the converter, C4, C5 and C6 must be increased to 2200uF.