Heathkit IT-12 Signal Tracer

This is a Heathkit Model IT-12 Visual and Aural Signal Tracer. This instrument is used to trace both audio and RF signals through a circuit to determine where a fault is. The silver probe has a switch that selects either audio or RF. When RF is selected, a diode detector and filter is placed in the circuit.
The audio or detected signal is passed to a 2-stage vacuum tube amplifier with a gain control mounted on the center left of the front panel (labeled Level). The amplified signal is then passed to a vacuum tube driver stage that drives the internal speaker.
A green "eye tube" in the lower left of the front panel gives a visual indication of the audio level. Stronger signals make the green eye segments come closer together.
The speaker and its audio output transformer can be used independent of the signal tracer to diagnose vacuum tube audio amplifiers by replacing the unit under test transformer and speaker. When the signal tracer is turned off, you can use the three binding posts in the lower right of the front panel to connect the internal output transformer to the circuit under test. The internal speaker is always connected to the transformer.
I purchased mine at a hamfest for a low price. The only thing wrong with mine is that the paint is flaking off the case. Otherwise it works perfectly. Even the eye tube is bright.