McIntosh MC275 MK V Tube Amplifier

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General:
A clean example of the famous McIntosh MC275 design, in its MK V designation next to the newest and current MK VI. The MK V was produced from 2009-2012.

The MK V sounds as good, if not better than the MK VI, and foregoes what many think to be silly LED lighting on the tubes and the more complicated speaker binding posts.

This amplifier was fitted with a set of strong pre-owned current production KT88 and 12AX7 tubes. New Old Stock GE JAN 12AT7 tubes were also fitted. 

Included along with the amplifier will be its original McIntosh box.

SkyFi Cosmetic Notes:
Some scratches on the chassis visible. Overall very presentable.

SkyFi Technical Notes:
This era of chassis from McIntosh has notoriously weak silkscreening that can lift even from basic cleaning. The lettering on this unit is missing in some areas.

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:
Single Owner

Connections:
RCA, XLR, Speaker Binding Post

General Sound:
Smooth, uncolored, undistorted natural and clean

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 and listening room.

Included:
Unit and box

Packing:
Original Manufacturers Packing

Specs:
75w/ch stereo into 4, 8 or 16 ohms,
150w mono into 2, 4, or 8 ohms
Response: 20-20kHz (+0 -0.5dB), 20-70kHz (+0,-3dB).
Distortion: 0.5%.
Noise & Hum: -100dB (A weighted).
Output Impedance: 4, 8, 16 ohms. (2, 4, and 8 ohms in mono).
Damping Factor: greater than 14.
Input Impedance: 90k unbalanced, 180k balanced.
Input Sensitivity: 1.2V unbalanced, 2.5V balanced.
Unity Coupled.
Power Requirements: 120V at 12 Amps.

Dimensions:
8-1/4"H, 12"W and 16-1/2"D

Weight:
67 lbs.

Approximate Age:
2009

Link to Manual:
Click Here

Recommended Cables:
Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - BALANCED XLR Connectors - Better

Kimber Kable - BALANCED XLR Connectors - Best

Kimber Kable - Speaker Cables - Better

Kimber Summit Series Monocle XL Speaker Cables (PAIR) - Best

Kimber Kable - Power Cords - Better

Kimber Kable - Power Cords - Best

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 resistors and other passive components for signs of overheating. If tube arcing has occurred in the past we can usually spot discoloration on the output tube sockets. On vintage units we often spot check select capacitors for value and ESR.

If the amplifier passes visual inspection, we move on to a full test of all of the tubes. We use a modern Amplitrex AT-1000 Professional Tube Tester which is capable of testing both emission and Gm with a high degree of accuracy.

We document the results of each tube and replace any weak or suspect tubes before proceeding.

When we power on tube amplifiers for the first time we usually use a variac and current limited AC supply and slowly raise the voltage up to nominal mains level while monitoring plate, screen, filament, and negative bias supply voltages where applicable.

If everything is in order we feed a low level test signal into the amplifier’s input and monitor its output on an oscilloscope across an 8 ohm dummy load. At this point we are just looking to verify basic function and confirm that the output transformers are not damaged.

Once we have verified that the amplifier is safe to operate, we connected it to full mains power. For fixed bias amps we set the bias to manufacturer spec. For cathode biased amps we monitor the plate to cathode voltage to determine if the output tubes are operating in a safe range. Once the output section is verified we move onto bench evaluation.

We start by feeding the input of the amplifier with a low level 1 KHz test signal, slowly increasing its amplitude while monitoring the amplifier’s 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 1 KHz square wave check and a 20 Hz to 20 KHz 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.

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 minimum.

For tube amps we like to run this test at least twice.

This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when it has fully come up to temperature. We find this step to be essential, especially for vintage units.