the variable resistance provided at terminals l and w the terminal h received 12 volts potential from dc film feed board the four stage linear dc amplifier board 30 is supplied by a dc power supply circuit 80 best seen in fig6 of the drawings the dc power supply circuit 80 is within the conditioning circuit 19 line voltage i e 120 volts vac is supplied to terminal l at 81 with respective terminals n neutral and g ground adjacent thereto a fuse 82 and surge protector 83 are provided as well as a pair of capacitors 84 a and b acting as high pass filters for incoming voltage a center tap step down transformer 85 drops the voltage from 120 vac to 35 volts for a low pass filter assembly of identical coils 86a and b and associated capacitors 87a and b providing one half 35 volt output to line 88 and one half 35 volt output to line 89 respectively a full wave bridge rectifier 90 and related capacitors 91a and b converts ac current to a flat dc voltage output voltage regulators 92a and b lock in 12 12 volts to a group of capacitors 93a b c and d that filter and clean up the dc signal an led and resistor combination 94 indicates state of board as either being on or off a coil and capacitor combination 95 acts as a second low pass filter with respective power output of 12 volt available at terminals p and p with a ground terminal g ground the dc power supply circuit also provides power to the respective strain gauges hereinbefore.