McIntosh MAC1900 The Original High-End Stereo Receiver - Serviced

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

General:
This is a super clean classic MAC1900 which was a great seller back in the 1970's.

Most MAC1900's suffer from having spent time in someone's damp basement resulting in light rusting, pitting, and component decay.

Not this one!

Condition is very good with little signs of use and some light scratches/scuffs.

The McIntosh MAC1900 is quickly becoming a great collectible piece, mostly due to its great features, solid tuner section, and amazing looks.

This tested well on our bench clean up to 60W per channel into 8 ohms. AM and FM bands were reviewed aligned, and all functions were tested and working to McIntosh original spec after our service.

SkyFi Service Notes:
• All multi-section capacitors tested for Value and ESR and replaced under chassis as needed.
• All electrolytic capacitors in preamp, power amp, power supply, and FM tuner replaced.
• AM board left original and working normally.
• Tone circuit rebuilt from scratch with new slider controls sourced directly from the McIntosh factory parts department.
- Tuner aligned.
- Lamps replaced as needed.

SkyFi Cosmetic Notes:
• Misc. light faceplate blemishes.
• Colored dots on push button controls are faded.

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:
Unknown

Connections:
RCA inputs, spring terminals for speakers, captive power cord. Coax antenna input for 75 ohms and spring terminals for 300 ohms. Convince power outlets (3).

General Sound:
Big beautiful musical sound with little fatigue.

Cosmetic Condition:
7/10 = Good. One or two minor scratches. Well Maintained. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab and listening room.

Included:
Just the unit and power cord.

Packing:
Original Manufacturers Packing

Original MSRP:
$949.00 in 1973. Close to $7,000 today after adjusting for inflation.

Specs:
Tuning Ranges:
FM and AM

Power Output: 
55 watts per channel into 8Ω (stereo)

Frequency Response: 
20 Hz to 20 kHz

Total Harmonic Distortion:
0.2%

Damping Factor: 
50

Input Sensitivity: 
2 mV (MM), 250 mV (line)

Signal to Noise Ratio: 
76 dB (MM), 90 dB (line)

Output: 
250 mV (line)

Speaker Load Impedance: 
4Ω to 16Ω

Dimensions:
W x H x D: 15.99" x 5.51" x 15" (406 x 140 x 381mm)

Weight:
33 lbs.

Approximate Age:
1974

Link to Manual:
Click Here

Recommended Cables:

Kimber Kable - RCA Interconnects

Kimber Kable - Phono Interconnects

Testing Process:

We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.

If the device has the ability to decouple the preamplifier from the power amplifier, we remove the jumpers and independently test each section. If the device cannot be decoupled, we assess the electronic condition of the piece by analyzing the speaker level output only.

We start by connecting the “preout” jacks of the receiver to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface. The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope. We then switch to a 1KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment. Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources.

If the preamp section is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve. 

To test the tuner, we connect one of the tape outputs to the Sencore PA81 and the antenna terminals to a Sencore SG80 which allows us to “simulate” an ideal radio station using precision test signals instead of music. This device, in conjunction with an oscilloscope allows us to properly evaluate the following parameters:

1. AM Reception (Where Applicable)
2. FM Mono Reception & Tuning Meter Function
3. FM MPX Reception (Stereo)
4. Dial Tracking - How accurately the tuner dial or display indicates the actual frequency of the broadcast being received.
5. Stereo Separation - A properly working stereo tuner will have minimal crosstalk between the left and right channel.
6. Sensitivity & Signal Strength Meter Function - By lowering the output of the SG80 we can simulate weak stations and determine how well the tuner will be able to pull in weak distant stations. This adjustment also helps us verify signal strength meter function.

If the tuner has acceptable performance related to the parameters above, we connect the unit for listening tests with a simple dipole antenna. We listen for audio reproduction quality of local stations and evaluate how many stations the tuner can receive while we sweep through the dial. We are looking to verify that the tuner can decode stereo on strong local broadcasts and pick up a wide variety of local stations at the bottom, middle, and top of the frequency band. At this point we also test convenience features such as muting, filters, built in oscilloscope function, etc. 

Next, we test the power amplifier section by connecting the receiver’s speaker outputs to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1KHz test signal at the “main in” jacks and slowly increase its amplitude while monitoring the output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance.We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.

If the preamp and power amp both pass these tests, we reconnect the sections and verify that the preamp section can drive the power amp to rated power with a 1KHz tone on one of the line level inputs.

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature.