McIntosh MPI-4 Maximum Performance Indicator - Serviced

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General:
The McIntosh MPI-4 is a valuable piece of HiFi for those that use FM Tuners. It's also relatively rare as only 1,792 MPI-4 were ever made from July 1973 through May 1977.

The MPI-4 is a laboratory-grade oscilloscope designed to measure multipath distortion from stereo tuners. Using the front controls you can also set the scope mode to L+R audio where the oscilloscope reacts to incoming signals which looks awesome!

It would make a perfect match for those using a vintage McIntosh tuner such as the MR78, but would also match well with any vintage setup.  

Best yet, this unit was just been serviced in-house for reliability and piece of mind. 

Please note the McIntosh MR78 FM tuner shown in some of our pictures is not included with this listing, but is available separately here for a killer vintage combination. The MR78 is considered one of the top three tuners of all time and for very good reason!

More from McIntosh:
The MPI 4 is a laboratory-grade instrument. It provides the facility to continuously monitor the quality of the performance of a stereo system. The MPI 4 can sample and display signals from the tuner, preamplifier and power amplifier without reconnecting cables. Signals are displays on an oscilloscope screen calibrated with scales for tuning, measuring and testing.

As a tuning aid, the instrument is a guide to exact FM station selection and precise tuning. The screen displays FM signal strength, modulation percentage and mulitpath interference. Audio signals may be viewed for stereo balance, strength, phase and channel separation. Output power of the power amplifier can be seen at any instant during program performance, or stored to develop a trend over several minutes.
With the addition of test records, the MPI 4 can show compliance and trackability of a phono pickup, frequency response of the preamplifier and power amplifier, audio distortion and stereo speaker balance.

In one of its operational modes, the MPI 4 becomes a "dual trace" oscilloscope. When operated in the dual trace mode the left and right stereo channels appear simultaneously and separately on the screen for direct comparison. The instrument also has "triggered sweep." It permits the viewer to choose a single tone and lock it on the screen for careful inspection.

SkyFi Cosmetic Notes:
This unit received a new glass faceplate. The text backlighting may appear slightly dimmer compared with the original 1970's era glass due to changes in production over the decades since. Light blemishes are present on all surfaces. Overall presentable.

SkyFi Technical Notes:
On initial inspection of this unit we noticed it was previously serviced.

The known to fail parts in the power supply were replaced. We took the unit one step further by replacing the power cord and all of the failure prone ROE caps in the deflection circuits.

After updating the parts, we performed a full alignment on the unit. With everything aligned properly, almost no adjustment is needed when switching between the various front display options.

One interesting feature of the MPI-4 that is not present in the earlier MPI models is a front panel variable gain control. This control is integrated with the power switch so its important to note that you must set your desired gain each time you turn on the unit. This tripped us up a couple of times during testing initially.

Brand Background:
McIntosh Laboratory is an American manufacturer of handcrafted high-end audio equipment based in Binghamton, New York. The company was founded in 1949 by Frank McIntosh. The company designs and produces audio amplifiers, stereo tuners and other consumer electronics products.

Ownership:
Second Owner

Connections:
RCA, Amp input terminals, AC outlet, Captive power cord

General Sound:
N/A

Cosmetic Condition:
8/10 = Very Good. Excellent front faceplate, one minor flaw on chassis side or top. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab.

Included:
Unit, original owner's manual, original sales brochure, and the (captive) power cord.

Packing:
Will be packed using our highly developed in-house process and custom packing materials.Specs:
Multipath Mode:
- Sensitivity: 100mV/cm
- Response: DC to 50kHz (–3dB)
- Input Impedance: 250kΩ
- Signal Strength Polarity: Positive or negative

Stereo Mode:
- Sensitivity (vertical and horizontal): 1.75mV RMS/cm (5mV p-p/cm)
- Response: 5Hz to 50kHz (–3dB)
- Input Impedance: 250kΩ

Power Level Mode:
- Sensitivity: 0.1 to 1000 average watts for full-scale indication (+3dB)
- Calibration: 9 calibrated steps
- Response: 5Hz to 100kHz (–3dB)
- Input Impedance: 75kΩ
- Load Calibration: 4, 8, and 16 ohm loads

Preamp Mode:
- Sensitivity: 15mV RMS for +3dB indication
- Response: 5Hz to 50kHz
- Input Impedance: 250kΩ

Sweep Mode:
- Display Modes: Left, right, or dual trace
- Sensitivity: 1.6mV RMS/cm (4.5mV p-p/cm)
- Response: 5Hz to 50kHz (–3dB)
- Input Impedance: 250kΩ
- Sweep Frequency: 20Hz to 20kHz in 3 decade ranges
- Sweep Expansion: 0.25X to 5X
- Sweep Triggers: Only when signal is present; selectable trigger channel in dual trace mode
- Level Mode Times:
- Normal: 250µsec rise, 500ms decay
- Peak: 500µsec rise, 25 sec decay
- Reset: 250µsec rise, 100 sec decay

Low Pass Filter:
- 16kHz LF filter for stereo and sweep modes
- 19kHz and 38kHz signals rejected by 30dB

CRT (Cathode Ray Tube):
- 3" round tube
- Calibrated display area: 5 x 6 cm

Reticle Lights:
- Multipath: Blue
- Stereo: Red
- Level: Amber
- Sweep: Green

Power Requirements:
- 120 Volts at 50 watts

Dimensions:
5-7/16" H, 16" W and 13" D

Weight:
21 lbs.

Approximate Age:
1973

Link to Manual:
Click Here