SCR-625 Adjustments

The amplifier and control box must be adjusted periodically, as the battery voltage changes and if control boxes or amplifiers are switched. In the description below, by adjusting for minimum audio output, I mean adjusting the control to a point where adjusting in either direction causes a louder audio output. If you adjust a control to the point there is no longer any audio output, then adjust the battery compensator clockwise until a tone is heard again, and continue with the control adjustment.

Typically the top of the "Coarse Adjust" screw is one tenth of an inch (2.5mm) below the top surface of the control box. If the batteries are near their nominal voltages (103 and 1.5 volts), the battery compensator control should be set near "5". To far beyond that, and the mine detector may start to squeal.

Note: Some of the amplifier boxes do NOT have a power switch for the 103 volt battery. ALWAYS remove batteries when you are done using the detector. The 1.5 volt "D" cells are prone to leaking and corrosion.

May 2013 note - When inserting the 103 volt battery into the amplifier box, place the positive end in first, push the negative end down last.

It may be necessary to try these steps several times over, especially for your first setup, or if the coarse adjust is way off.

If you are having trouble getting any vintage electronics working, I want to emphasize trying and retrying all connections: cables, tubes and batteries. If it is not working right, disconnect and reconnect all physical connections, and jiggle connections with power on when possible, to see if it changes.

Initial Setup, or if control boxes are swapped:

1. Set fine adjustment knobs on the control box to the middle of their range.

2. Remove coarse adjustment cap from control box with medium size screwdriver.

3. Turn power on the mine detector and adjust battery compensator knob clockwise until a moderately loud signal is heard.

4. Adjust screw inside control box with small screwdriver for minimum audio out. Readjust battery compensator control higher if need be, to find the best setting.

5. When minimum audio output is heard, replace cap over coarse adjustment control.

6. Go to normal adjustments.

Normal adjustments:

1. Turn power on the mine detector and adjust battery compensator knob clockwise until a moderately loud signal is heard.

2. Alternately adjust the fine control knobs until the minimum audio output is heard. Readjust battery compensator control higher if need be, to find the best setting.

3. If you reach the limit of adjustment and the minimum output is not achieved, go to the Initial Setup procedure.

4. Once minimum output is achieved, adjust the battery compensator knob counter-clockwise until there is no tone or minimal tone.

5. The mine detector should now be ready to use.