18.5 turn aluminium strip coil to suit gap with wooden tripod support, part of Oliver Lodge’s microphone amplifier or relay, 1898 (British patent 9712 of 1898) ), a precursor of the moving-coil loudspeaker
18.5 turn aluminium strip coil to suit gap with wooden tripod support, part of Oliver Lodge’s microphone amplifier or relay, 1898 (British patent 9712 of 1898) ), a precursor of the moving-coil loudspeaker
