heathkit groundtrack gr 1290 vlf metal detector schematic
heathkit groundtrack gr 1290 vlf metal detector schematic Heathkit Groundtrack GR1290 metal detector schematic It had a diameter of around 15cm (6 inch). A larger (30cm, 12inch) coil can be made using the following data: L1 = 300mm diameter, 90 turns, .4mm wire. L2 = 140mm diameter, 90 turns, .4mm wire.