The power supply stabiliser circuit is shown in Fig. 12. Here the diode D5 will prevent damage if incorrect connection to the power source is made. The supply to the main amplifier and multivibrator is taken from the Zener diode D4, and that for the meter circuit is additionally decoupled by R33 and C21.

Three separate chassis connections, G1-G3, are made between the main amplifier and stabiliser to prevent the possibility of oscillation.


The supply lead from the 12V battery must be screened. The centre wire is positive and terminates at SK5; the negative screen at SK6. Constructional details are given in Fig. l3. Since the magnetometer draws about 750mA during “polarise”, an adequate heavy duty power source must be used.

CHASSIS ASSEMBLY

Assembly details of the modules on the chassis and front panel interwiring is given in Fig. 14. It should be emphasised that the chassis must he aluminium, and contain as few iron parts as possible, ideally none.