From an old ad:
Full, accurate use of station WWV, the world's finest primary frequency and time standard, is obtained from the Browning Model RH-10 Standard Frequency Calibrator. The standard Browning RH-IO is pre-tuned for 5 and 10 megacycles per second reception, at sensitivities better than 1/2 microvolt on either band. A dual filter system provides selection of either the 440 or 4000 cycle modulation of WWV for use as a primary frequency standard.
Checking equipment against station WWV, at accuracies up to one part in five million, the Browning Frequency Calibrator enables comparisons to be made in three general categories:
I. Precision radio frequency standards measurements.
2. Precision audio frequency standards measurements.
3. Precision time and pulse standards for physical measurements.
The Browning RH-10 consists of a high Q antenna transformer, a sharply tuned R -F amplifier, converter, oscillator, two IF stages, detector, selective amplifier output stages and a cathode ray zero beat indicator. Although normally supplied
for 5 and 10 megacycles per second operation, any two combinations of 2.5, 5, 10, or 15 megacycles may be had on special order.
Looks like fun! I suppose 440Hz was for the musically inclined (note A4, first A above middle C on the piano) although it is also an ISO standard.
This will be all of vacuum tube construction and also has a CRT so there will be high (deadly) voltages present. I wouldn't work on it unless I had an experienced person to help.
73, Mark