Maker's Name: 
General Radio Company Concord Mass.
Where made: 
23.5 × 30.5 × 19 cm

Test instrument provides a random noise signal over audio, long wave and middle wave frequencies.

A filamentary diode valve 6D4 in a magnetic field generates a noise signal that is amplified by two 6AQ5 stages.

A 0.3A, 4V ballast maintains the 6D4 filament current constant.

A 115NO3OT thermal delay valve allows the noise diode to heat up and settle first.

Ranges: 20 kc/s, 500 kc/s, 5 Mc/s.

Output 0.0001, 0.001, 0.01, 0.1, 1.0

Meter FSD 5V in 0.2 V steps.