A thermostat set for selective connection with a center tap transformer and a temperature control device operator and to be selectively assembled to provide a thermostat with or without a control switch. The thermostat set includes a base including first through fourth electrical terminals and having a bridge circuit thereon which includes first and second resistance means formed with a node at their common end. The first resistance means is in the form of a temperature sensor. The base circuit includes rectifier means having its gate connected with the first node, lead means connecting the free end of the first resistance means with the first electrical terminal and the free end of the second resistance means with the second electrical terminal and the power circuit of the rectifier means with the third and fourth terminals. A first sub-base is provided which includes first and second input terminals for connection with opposite sides of said transformer and a third input terminal for connection with the center tap thereof, such sub-base further including first through fourth output terminals. A first sub-base circuit connects the respective first through third input terminals of such sub-base with the first through third output terminals thereof and the second input terminal with the fourth output terminal thereof. A second sub-base also includes first through third input terminals and first through fourth output terminals and second sub-base circuit means connects the first through third input terminals with the respective first through third output terminals and the second input terminal with the fourth output terminal. The second sub-base circuit further includes switch means for breaking the circuit through such second sub-base. Electrically conductive mechanical connector means is provided for selectively connecting the first through fourth terminals in the sub-base with the respective first through fourth output terminals of the respective first and second sub-bases whereby a workman may select either the first or second sub-base for assembly with the base to thereby provide a thermostat with or without switch means depending upon the requirements of the particular installation.
