Vacuum tube driven audio has become almost completely obsolete from modern audio equipment and is maintained only by a handful of companies. Most audiophiles lean towards this anachronistic method of driving audio because of the signature quality that only tubes can produce. Vacuum tube audio systems, by their very design, introduce distortion into the audio signal. This would typically be frowned upon, but the distortion present in tube-driven units is particularly harmonic to the human ear and thus often preferred by audio aficionados.
I very recently acquired a vintage McIntosh product that I am extremely proud of. This particular unit was introduced in 1964 and is known as the MI3 Maximum Performance Indicator. The MI3 is extremely rare today in the sense that the technology utilized within the unit is completely obsolete and that the instrument itself is difficult to track down given its age and the specific nature of its utility. The MI3 is a passive instrument, which is to say it does not affect the audio signal that is subject to. Rather, the MI3 is an audio-testing unit; designed to visually represent an audio signal. The MI3 achieves this objective via the use of a cathode ray tube, which is in turn driven by vacuum tube technology. When all the shiny paper and complicated descriptions are pealed away, the MI3 is an oscilloscope, no more & no less. The instrument allows the user access to a variety of different features, most notably the ability to monitor and thus reduce multipath. The MI3 was designed to be used in conjunction with a tuner; allowing one to tune more accurately and be aware of the presence or lack of multipath. The MI3 is also capable of displaying reversed polarities, out of balance audio sources, & missing channels. When a source is accurate in its representation of a stereo signal, the screen of the MI3 is filled with dancing glowing lights, a beautiful and chaotic interpretation of the present audio signal.
While the MI3's usefulness in acquiring top-end audio clarity is minimal at best (especially the tuning utility), itself and units like it have become collectable for their use of cathode ray tubes. The technology is beautiful and just plain cool to look at. The build quality of the MI3 is top notch, as would be expected with any McIntosh product. The use of black glass and anodized gold font beautifully dates the unit, as do the silver pots.
The McIntosh MI3 Performance Indicator is two things: a rare and elegant electronic instrument produced by one of the most respectable audio houses in the world & quite literally, a visual and design-based representation of 1960s technology.