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General Radio 724-B
Precision Wavemeter
General Radio 724-B Precision Wavemeter

Available from 1948 to 1954

Catalog History
 Document Year Page
Catalog L 1948 194
Catalog M 1951 216
Catalog N 1954 223
(All manuals in PDF format unless noted otherwise)

The General Radio 724-B Precision Wavemeter was introduced in Catalog L (1948) and remained available through Catalog N (1954). The primary application of the 724-B is oscillator and transmitter frequency measurement.

The Type 724-B is an absorption-type wavemeter with a range from 17 kHz to 50 MHz using seven coils with an accuracy of ±0.25%. The capacitor used is similar to the Type 722-N 722-N Precision Capacitor. It is connected to the inductor through a Type 774 coaxial connector.

Resonance is achieved using one of three methods – absorption method, reaction method, or beat method. Using the panel microammeter, the absorption method is employed. Regardless of the method, once resonance is achieved, it is a matter of using the correct chart for the coil in use to determine the measured frequency.

The Type 724-B was supplied as a collection of calibrated components – capacitor, inductors, and calibration charts – sharing the same serial number, and they must have the same serial number to achieve the stated accuracy.

The 724-B replaced the 724-A Wavemeter. The principal difference is that where the earlier version used a vacuum tube rectifier, the 724-B uses a 1N34 crystal rectifier. The "A" version required a battery, the "B" version does not. The wavemeter was furnished with a wooden storage case, fitted with lock and carrying handle. This case has compartments for holding the capacitor, inductors, and calibration charts.


  • Frequency Range: 17 kHz to 50 MHz using seven inductors
  • Accuracy: ±0.25%
  • Inductors: 7 coils wound on steatite forms and enclosed in molded phenolic cases
  • Capacitor: Precision worm-drive type similar to Type 722
  • Resonance Indicator: microammeter and 1N34 crystal rectifier combination