Note
Service magazine, Aug 1937, p. 489.
Radio's Master Catalog, copyright 1937, p. F-19.
Radio Craft, Oct 1937, inside front cover.
From the ad:
"Complete with built-in horizontal and vertical amplifiers. Utilizes the full-size 3" screen cathode ray tube. Used for measurements of AC wave forms, frequency, phase, tube characteristics, hysteresis, hum distortion, AC peak volts, overload of AF or IF amplifiers, vibrators, transmitters, etc. Use with RF signal generator for visual alignment work."
References
Technical description. Radio Craft, Jun 1938, p. 805.