For each of the instruments described below I have listed the prices shown in the GR catalogs in my collection.  Catalog O (Jun-1956) and Catalog T (Feb-1968) are online at the BoatAnchor Manual Archive.

A microvolter is used with an audio oscillator to provide low-level audio signals of known voltage.  Frequency response is 20 Hz to 20 kHz, with measurements possible to 100 kHz with reduced accuracy.  With a standard input voltage of 2.2 V output voltage range is 0.5 μV to 1.0 V.  Input impedance is a nominal 600 Ω, and output impedance is a nominal 600 Ω ±5%.  Basic accuracy is ±3%.  Prices in GR catalogs: L (1948) $110.00, M (Oct-1951) $125.00, N (Jan-1954) $125.00, O (Jun-1956) $135.00, P (Apr-1959) $140.00, Q (May-1961) $155.00, R (May-1963) $180.00, S (Jul-1965) $195.00, T (Feb-1968) $250.00.

This instrument was primarily used by broadcast and recording engineers to measure audio levels on 500 Ω lines.  It covers the range from -20 dB to +36 dB, referenced to a 0 dB level of 6 mW into 500 &Omega.  The input impedance is 5 kΩ with no appreciable reactance.  Average accuracy is ±0.2 dB, and it is usable to about 10 kHz.  Mine doesn't have the original binding posts, but I have another GR instrument that is a junker and has the correct posts, which I'll transfer to the 586.  Prices in GR catalogs: F Part 3 (Oct-1931) $75.00, G (Dec-1932) $75.00.

Several related GR instruments, including the Type 760-B and the Type 1550-A Octave-Band Noise Analyzer, were predecessors to modern real time audio analyzers.  The Type 760-B was designed primarily for measurement of noise produced by electrical and mechanical equipment.  It operates from the output of a sound level meter, and uses a tunable high-Q filter to measure the amplitude of each individual frequency component of the noise.  Frequency range is 25 Hz to 7.5 kHz in five ranges.  Attenuation of the filter is 3 dB at ±1% of the center frequency and 25 dB at ±20%.  Frequency response is flat within ±2 dB.  Input range is from 1 mV to 10 V.  Prices in GR catalogs: N (Jan-1954) $520.00, O (Jun-1956) $520.00, P (Apr-1959) $520.00.

A beat frequency oscillator combines the output of two radio frquency oscillators, one fixed in frequency and one variable.  The resulting heterodyne is filtered to produce an audio frequency.  This results in an instrument that produces all audio frequencies from 20 Hz to 20 kHz in one range, and 20 kHz to 40 kHz in a second range.  Frequency calibration is ±1%.  An output meter and attenuator provide full-scale open circuit outputs from 50 mV to 50 V in four ranges.  The output impedance is 600 Ω, and maximum output is 1 W into 600 &Omega.  Distortion is less than 0.25% from 100 Hz to 10 kHz, and less than 1% over the rest of the frequency range.  Prices in GR catalogs: N (Jan-1954) $555.00, O (Jun-1956) $575.00, P (Apr-1959) $625.00, Q (May-1961) $680.00, R (May-1963) $795.00, S (Jul-1965) $850.00, T (Feb-1968) $1,075.00, U (Feb-1970) $1,275.00.

Several related GR instruments, including the Type 1550-A and the Type 760-B Sound Analyzer, were predecessors to modern real time audio analyzers.  The Type 1550-A was designed to analyze broad band noise in eight bands between 20 Hz and 10 kHz.  The input impedance is 20 kΩ and input voltage range is 1 V to 10 V.  Input was normally provided by a GR sound level meter.  Prices in GR catalogs: N (Jan-1954) $535.00, O (Jun-1956) $535.00, P (Apr-1959) $535.00, Q (May-1961) $575.00.

The Type 1932-A measures distortion, noise and hum in audio circuits and equipment.  Distortion as low as 0.1% can be measured on fundamental frequencies from 50 Hz to 18 kHz.  Residual hum and noise as low as 0.02% or -80 dBm can also be measured.  Basic accuracy is ±5%, and input impedances are 10 kΩ balanced or unbalanced fo 600 Ω circuits, and 100 kΩ unbalanced.  This instrument was frequently used for AM broadcast transmitter measurements as a companion to the matching Type 1931-A Amplitude-Modulation Monitor.  Prices in GR catalogs: L (1948) $575.00, M (Oct-1951) $595.00, N (Jan-1954) $595.00, O (Jun-1956) $620.00, P (Apr-1959) $650.00, Q (May-1961) $725.00, R (May-1963) $795.00, S (Jul-1965) $850.00.