RI (Radio Instruments)
Dual Range Coil
Popular Wireless and Modern Wireless were magazines available in the 1920s. Each edition was full of construction details for building the latest wireless set. This dual range coil was specified in those magazines for use in a number of their circuits. It also featured heavily in a booklet entitled ’77 Selected Circuits’ published in the early 1930s. The advert shown below is from that booklet.