Skip to content


Your cart is empty


Subscribe to receive updates, access to exclusive deals, and more... We promise not to give your info away.

McIntosh MI-3 Tuner Maximum Performance Indicator

Sale price$0.00
Free Shipping on *ALL* Electronics (Excluding Speakers, Contiguous 48 US States Only)

Pickup currently unavailable at SkyFi 479

Mcintosh Mi-3 Tuner Maximum Performance Indicator Accessory

McIntosh MI-3 Tuner Maximum Performance Indicator

SkyFi 479

Pickup currently unavailable

479 South Broad Street
Glen Rock NJ 07452
United States


If you have a McIntosh vintage tuner then this accessory is an absolute must!

The built in oscilloscope illustrates the performance of the signal, which also happens to be incredibly entertaining to watch!

This example is the cleanest we have ever seen, and also very rare.  These are usually found with a faded 3" CRT display tube, or damaged glass which is no longer available from McIntosh (or anywhere).

This display tube is super bright and responsive, the glass is free from cracks, and the cabinet work is rust free with great paint quality.

*Note this MI-3 is actually tube powered - VS the later model solid state MPI-4.

More Information from the McIntosh Owner's Manual:

The Mclntosh Ml 3 is five laboratory instruments combined into one compact instrument. It is a professional oscilloscope, relative signal strength indicator, calibrated FM deviation meter, calibrated balance meter, and phase indicator.

These instruments are used by FM stations to determine the best possible performance for your listening enjoyment.

The Mclntosh Ml 3 Maximum Performance Indicator makes it easy for you to attain professional broadcasting quality FM listening.

The Mclntosh Ml 3 shows you what you need to do to improve your system's overall performance. It is designed to be used with an FM tuner and stereo preamplifier.

When the Ml 3 is used with an FM tuner it will detect and display multipath reception. Multipath reception is the result of a reflected signal arriving at the tuner antenna slightly later than the direct signal. By rotating or repositioning your FM antenna it is possible to reduce the multipath reception. The Ml 3 Maximum Performance Indicator makes it easy to know when the FM antenna is oriented for the best reception of any station.

To show multipath reception the Ml 3 displays instantaneous signal strength versus frequency deviation. Signal strength is shown as vertical deflection of the indicator display beam. Frequency deviation is shown as horizontal deflection. Multipath reception appears as a peak or valley in the Ml 3 picture tube display.

The Ml 3 is a very effective tuning indicator:

1. Signal strength is shown by the vertical position of the display trace. The higher the position of the trace the greater the signal strength.

2. Correct tuning occurs when the display trace is centered hori- zontally on the screen. Since the display trace effectively follows the tuner I.F. response curve, centering the trace tunes the de- tector to the center of the I.F. curve.

The Ml 3 Maximum Performance Indicator is a versatile instrument.

When used with either a stereo preamplifier, or power amplifier the Ml 3 when switched to the L+R AUDIO position will show you the character of the audio signals present. The Ml 3 will:

1.  Display a trace along the L+R line when a monaural program is playing.
2.  Will display along the L—R line when a monaural program source has one channel out of phase.
3.  Display a vertical trace if only the left channel is being de- livered.
4.  Display a horizontal trace when only the right channel is being delivered.
5.  Helps you set the precise balance of your system. With the bal- ance control you can change the angle of the L+R or L — R display.
6.  A stereo program will be a complex and varying circular or elliptical display of irregular outline that depends on channel separation or on the phase amplitude relation of the left and right channel.

MI3 Specifications:

Signal Strength (vertical) Input:
— 700 MV
Left Audio (vertical) Input:
20 MV
Deviation (horizontal) Input:
±350 MV
Right Audio (horizontal) Input:
20 MV

Front panel:
16 inches wide by 5-7/16 inches high

Chassis (including PANLOC shelf):
15 inches wide by 5 inches high by 13 inches deep, including connectors

Clearance in front of mounting panel, including knobs:
1-1⁄2 inches

1— 3RP1, 3 inch cathode ray tube
4— 6EA8, horizontal and vertical deflection amplifiers
1— 6EA8, electronic voltage regulator
2— OB2, voltage regulators
1— Selenium rectifier, high voltage rectifier
6— Selenium rectifiers, low-voltage supply
4— Silicon planar transistors

Chassis only, 23 pounds
In shipping carton, 30 pounds

Anodized gold and black glass front panel

50 watts, 105 to 125 volts
50 to 60 cycles

1 Ampere Slo-Blo

Click here for a PDF copy of the original McIntosh MI-3 Owner's Manual

Click here for a PDF copy of the original McIntosh MI-3 Service Manual

Please click here for detailed specifics regarding our specialized packing process that separates us from the rest.



Original Box







Yes - Power

Physical Condition


Working Condition


SKU: 100450