ID: 
2500
Maker's Name: 
General Radio Co., Cambridge, Mass.
Where made: 
USA
Dimensions: 
31 × 27 × 20 cm

Audio frequency null detector or output meter. A two-stage linear amplifier drives the null detector. A 1D8GT valve is used in the null bridge circuit. A third amplifier stage may be added to provide a logarithmic output to the meter. Sensitivity can extend to 25 ┬ÁV input. The meter is a Weston Model 891.