• Power output of oscillators, amplifiers, preamplifiers, transformers, transducers, and low-frequency lines.
  
• Output impedance, by adjustment of the load to yield maximum power indication.
  
• Frequency-response characteristics of amplifiers, transformers, and other audio-frequency devices.

This instrument is basically a multi-tapped audio-frequency transformer with a fixed secondary load. Its two front-panel switches connect eight identical primary windings and six secondary taps in various combinations to provide a total of 48 different primary impedances.

The maximum power rating can be extended for any given impedance with the use of simple T-network attenuator, design data for which are supplied with the instrument.

General Radio 1840A Output Power Meter (in .pdf format)