This 12 VDC to 240 VAC Inverter circuit are not using special components such as the torodial transformer found in many inverters circuit. Inexpensive and components are easy to find.
Essentially, it is a power amplifier driven by an astable multivibrator. The frequency is around 1200 Hz which most 50/60 Hz-power transformers handle well without too much loss. Increasing the value of capacitors C1 and C2 will lower the frequency if any trouble is experienced. However, rectifier filtering capacitors required are considerably smaller at the higher operating frequency. The two 2N3055 transistor should be mounted on an adequately sized heatsink. The transformer should be rated according to the amount of output power required allowing for conversion efficiency of approximately 60%.
12 VDC to 240 VAC Inverter Parts list :
R1, R2 : 15 K R3, R4 : 220 ohm C1, C2 : 0.047uF/50 V Q1, Q2 : 2N3638A Q3, Q4 : 2N3055