MA 101 – Operation (Figure 211)

Arming. When the mine is dropped, action of the Rheinmetall fuze closes the master switch F, making one contact and breaking two. Thermostatic switch A is normally closed at temperatures between 23° and 95° F. B1 energizes fuse delay-switch No. 17 which, upon completion of its delay period, cuts in fuse delay switches No. 18 and No. 22. Hy-drostatic switches H1 and H2 open when the mine reaches a depth of 15 feet or more. Upon completion of its delay period, switch No. 18 switches over, cutting in switch No. 19 which, upon completion of its delay period, connects the battery to the main positive and negative terminals of the unit.

The magnetic component (M 103 unit slightly modified) then goes through A.L.A., upon the completion of which the onyl parts of the magnetic component remaining in the circuit are W6, Lr or Lb, and K. During A.L.A., switches No. 20 und No. 21 operate, swit-ching in the P.D.M. fuse-delay switches and breaking the negative return contact to the magnetic component.

Delay-Action Bomb Firing. Two different methods of accomplishing delay action bomb firing may be employed as follows:

1. if the mine does not reach a depth of 15 feet H1 remains closed and, when fuse-delay switch No. 22 switches over, a detonator is put across the battery and the mine fires.

2. If the mine does not reach a depth of 15 feet, H2 also remain closed. When fuse delay switch No. 19 switches over and connects the battery to the positive and nega-tive leads of the unit, switch No. 23 will operate and fire the mine if H2 has not opened. (H2 is provided to allow an alternateive method of delay bomb firing in case H1 does not operate properly.)

Normal Firing with P.D.M. A RED or BLUE actuation will close K to contact No. 1 or No. 2, respectively, and current will then pass from the main positive lead through W6, Lr or Lb, K, thermistor Y, and the normally closed contact of thermal delay switch D; and the operating coils of relays R1 and R2 close. Closing of R1 provides a self-holding circuit for R1 and R2 through the contact of D. Cloring R2 energizes the heater of D, energizes the four microphones M through W2 and energizes the vacuum tube filament through W3. The self-holding circuit of R1 and R2 shunts out the needle system, reducing the hold-on current to such a low level that K breaks its contacts and Y cools. The main circuit through R1 and R2 will persist until D breaks its contact due to heating action.

If sound impinges on the microphone before D breaks its contact, the change in microphone resistance appears as current variations in transformer T1 and passes through the filter circuit to the control grid of pentode V. This vacuum tube amplifies the signal, which then appears as current variations on transformer T2. The output of T2 is fed to the operating coil of sensitive relay R3. Since the rectifier X1 allows current to pass only in the direction of its arrow and since the current output from T2 is alternating, X1 passes current half the time to the operating coil of R3 with a slight delay due to C6. Rectifier X2 acts as an overload feature to by-pass heavy currents. The signal current from T2 and X1 closes R3 to contact No. 1.

When R3 closes to contact No. 1, a circuit is completed from (+) through the by-passing fuse of fuse-delay switch No. 1, the holding coil of R3, and thermistor Z to (-). If the  sound persists long enough, Z heats and passes enough current to operate the holding coil, the by-pass fuse blows, and fuse-delay switch No. 1 carries the total load until completion of its delay period, when it switches over to switch No. 2, thereby cutt-ing out the holding circuit and allowing R3 and Z to return to normal. Before switch No. 2 completes its delay period, D breaks its contact, cutting out R1 and R2 holding circuit, its own heater current, the microphone current, and the vacuum tube current. When switch No. 2 switches over to No. 3, the entire unit is again normal and ready for re-actuation. A maximum of eight "blind" actuations operates switches No. 15 and No. 16, putting the detonator in the circuit, and an additional magnetic-acoustic actuation fires the mine.

P.S.E. Firing. If water or excessive moisture enters the unit, a cell is formed between two dissimilar metals. Current will flow through the operating coil of R3 in such a direction that R3 closes to contact No. 2, making a complete circuit from (+) through the closed contacts of switches No. 18 and No. 19, a detonator, the R3 holding coil and Z to (-). When Z has heated sufficiently, the current holds the relay closed and the mine fires.

Figure 211 – MA 101 Unit Circuit