A 105 Circuit Operation (Figure 185)

Arming. When the mine is dropped, action of the Rheinmetal fuze closes the master switch F. Since the thermostatic switch E is normally closed between temperatures of 23° and 95° Fahrenheit, B1 energizes the microphone M through W1 and fuse-delay switch A. Upon completion of its delay period, A switches over, putting B2 in the circuit.

If the mine reaches a depth of 24 feet or more, hydrostatic switch G closes to con-tact No. 2, and, upon completion of the operations described above, B2 energizes fuse-delay switch B. Upon completion of its delay period, B switches over, cuts itself out, and puts the detonator in the circuit. B2 charges C4 after a 15-second delay due to the re-sistance of W6.

Delay-Action Bomb Firing. Same as A 104, except that all current is supplied by B2.

Normal Firing with P.D.M. When sound impinges on the microphone, the change in microphone resistance appears as current variations on the primary of the transformer T, and as alternating signal current on the secondary of T. The signal current is rectified by X1 and X2 with direct current then flowing through R1 and R3, charging C3. R1 is more sensitive than R3, the sound level at which R1 operates being the initiating level and the level at which R3 operates being the firing level.

When the sound reaches the initiating level, R1 closes r1, causing C4 to start charging C5 in an attempt to operate R2. After 1/2 second, C5 will be sufficiently charged to ope-rate R2, thereby breaking r2a, and making r2b. If the sound then reaches the firing level before C4 and C5 discharge (10 seconds), R3 closes r3, completing a circuit through fuse-delay switch No. 1, r2b, r3, W9, r1, and W3. Potential drop through W3 holds R1 and R3 operative, and since r1 is held closed, C4 and C5 hold R2 operative.

Upon completion of its delay period, switch No. 1 switches over, cutting in switch No. 2 and by-passing the holding circuit which, if the sound has ceased, allows the cir-cuit to return to normal. Upon completion of its delay period, switch No. 2 switches over, cutting in switch No. 3, and the circuit is normally alive again. After a maximum of nine "blind" actuations, switches No. 17 and No. 18 operate, putting the detonator in the firing circuit; and an additional actuation will fire the detonator.

Normal Anti-countermining. Normal anti-countermining may occur if the sound level rises too fast. The unit will be rendered passive in the same manner as the A 104, except that if the sound ceases or drops below the firing level, the unit will not again be nor-mally alive for a period of 15 seconds maximum.

P.S.E. Firing. Photo-electric cells may be fitted as in M 101.

Figure 185 – A 105 Unit Circuit

Figure 186 – A 105 Unit