connected to drive member 31 of an on off control switch 26 to be more fully described hereinafter switch 26 is mounted on a printed circuit board 24 which is entrapped in the space formed between cover 20 and rear iron wall 22 printed circuit board 24 is snapped into a suitable potting frame 25 thereafter a potting compound is used to encapsulate the electric components on board 24 the frame is then connected to rear wall 22 referring now to fig2 6 there is shown a preferred embodiment of switch 26 switch 26 includes a non conductive housing 30 formed from suitable plastic or other similar material housing 30 includes a pair of rectangularly shaped spaced housing blocks 74 and 76 for mounting terminal pins 36 and 38 respectively terminal pins 36 and 38 are connected to board 24 an electrically conductive winding 32 is supported within the space between housing members 74 and 76 each end of winding 32 is connected to a respective terminal 36 or 38 so that when electrical power is supplied to the terminal winding 32 is energized a nose piece 29 extends outwardly from housing member 76 nose piece 29 has a bore 27 extending therethrough a metallic drive member 31 extends within bore 27 drive member 31 includes a first cylindrical portion 28 and a second cylindrical portion 34 of a somewhat larger diameter than portion 28 as shown in fig1 cylindrical portion 28 of drive member 31 abuts stem 15 of control knob 16 and is therefore movable within bore 27 in response.