BC221 AF Frequency meter manufactured by Zenith Radio for the American Army Signal Corps. Unlike most frequency meters this incorporates a signal generator with a crystal controlled oscillator and a variable frequency oscillator together with a a detector, mixer, LF oscillator and amplifier. It can therefore be used to calibrate receivers and transmitters. It comes complete with a multi page calibration book housed in the front cover door. Order number CZR/29307 Phila. 43 (the CZR refers to Zenith Radio) Chicago USA 1943

Converted to use 240v Mains plug UK