Boonton Model 260A Q-Meter

Although Boonton company made a number of Q-meters, the 260A probably represented the state of the art. With two meters, it is straightforward to "dial in" the device under test and read out the Q with great accuracy. It is a remarkable device. The first part of it is a power oscillator that goes from 50 kHz to 50 mHz in 8 ranges. Looking at it on the 'scope shows it to be a very pure sinusoid at all ranges. If you have ever looked at the VFO output in a general-coverage receiver, you will know that purity across all bands is something of a miracle. The amplitude of the oscillator output is controlled by a dual wire-wound rheostat that controls the screen voltage (!) of the oscillator. To get the true RMS current through the DUT (Device Under Test) over all frequencies, the 260A uses a thermocouple (!) that drives a microammeter. An amazing piece of engineering. I don't think there is anything on the market today that does what this device can do.