This is a portable converter and is intended for use with a 12 V lead- acid battery. Whether it’s in the car, boat, caravan or mobile home, this converter provides a mobile 220 V a.c. supply suitable for powering small electrical appliances, such as lights, soldering irons or electrical tools. The circuit requires only ‘ six transistors, a mains transformer and some capacitors and resistors; An astable multivibrator (AMV), consisting of transistors T1 and T2, provides a square-wave at a frequency ofabout 50 Hz. As T1 and T2 conrjuct§ alternately, the output stages also operate in ‘push- pull”. When T1 conducts, a current also flows through T3; this switches on T5 and this transistor connects one half of the secondary winding, of mains transformer Tr across the 12-volt battery. if T2 conducts, transistor T6 switches the other half of the mains transformer across the battery. if RCA 40411 transistors are used in the output stages, the current through the secondary wind- ing can be as high as 10 A, giving a possible power output of 180 watts. If 2N3055 transistors are used, the power output will be about 90 watts. As the output transistors are driven into saturation, they should be mounted on very large (100 mm high fins) heat-sinks. If a toroidal mains transforrner is -used, the , converter can be constructed as a very compact unit. The advantages of a simple construction and high efficiency are set by the disadvantage of a wave output voltage which, in absence of a regulator is load dependent: at low loads the output may be well over 220 VAC. This presents no problems for small electrical appliances, but drills electronic speed control or light dimmers may, not work effectively as they are designed for sine-wave- operation only. lt is definitely not advisable to try to operate colour’ television sets, video recorders or HiFi equipment from this.