This converter was built from plans in an April, 1928 issue of Popular Radio and Television. It is designed to receive short wavelengths used for television broadcasting.  The converter has a 4 pin plug which is inserted into the detector tube socket of a standard broadcast band radio of that era, and is designed using 1 tube (201-A) in a regenerative type of circuit. The front knob controls tuning (it uses a National Velvet Vernier drum dial, Type F) while the small knob on the side controls regeneration. Here is a 1929 converter and a 1931 converter.