Hi Clondike Clad,
The only circuit I have seen for a LRL pickup system is shown in the schematic of Morgan's pistol detector drawn by Max. This schematic looks similar to the kind of pickup circuits we find in some old 2-box detectors. In order to build a pickup circuit, you could start with the pickup circuit shown in the Morgan schematic. From what I can see the missing information for the pickup coil is not too hard because there are only 3 wires that go to the pickup coils. Maybe 2 pickup coils, or a single coil with a tap in it.
If this doesn't work, then maybe you should look for some 2-box schematic to try, or other old metal detector circuit that has a similar schematic to the schematic Max made.
Best wishes,
J_P
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