McIntosh MC275 Mk III Tube Amplifier - New Old Stock Collectors Dream Piece

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General:
Featured in our most recent SkyFi YouTube video, this McIntosh MC275 is in new condition and never used.

It is a true time capsule. 

The MC275 is one of the most famous McIntosh tube amplifiers of all time featuring 75 watts of tube power. This piece is only expected to gain value over time. 

This specific MC275 is considered a Mk III, produced only from 1995 - 2003, and featuring a combination of point to point wiring and OC boards. It remains relevant by today's standards as it has XLR inputs as well as high quality RCA inputs.

This was stored in a temperature and humidity controlled unit for al these years. 

We recently received four different and very desirable NOS models from the same collector., but only this item was opened up to be featured in the video.  

Client can choose to take delivery as is, or have us open it up for testing and verification.  Regardless of choice, contents and condition are guaranteed.  We understand that a collector might want to keep the unit un-powered while someone that is going to use it might want it tested thoroughly.

SkyFi Cosmetic Notes:
Unit shows no signs of wear, brand new. Box is very good.

SkyFi Technical Notes:
This amplifier does include vacuum tubes. If you would like to purchase a curated set of tubes from our collection, please select from menu.

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:
Zero - New Old Stock (NOS)

Connections:
XLR, RCA, Speaker Binding Posts

Cosmetic Condition:
NOS, unused since it left the factory and left sealed until we made this recent video on our YouTube for this listing. See our detailed rating description here.

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

Included:
Complete Kit as it Left the Factory

Packing:
Original Manufacturers Packing

Testing Process - if Selected:
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.