McIntosh MC-275 (1961–1970)
Sixty-seven pounds of tube power that McIntosh keeps bringing back from the dead - the "Stereo Power House" that refused to stay retired.
Overview
The MC-275 debuted in 1961, and in its original hardwired edition it stayed in production until 1970. That first run is the one collectors talk about. It set the amplifier's reputation: two 75-watt channels on a single compact chassis, built around McIntosh's patented Unity Coupled Circuit and a bifilar-wound output transformer. High Fidelity (December 1965, p.156) called it the "Stereo Power House" - two 75-watt amplifiers on one chassis, with typical distortion of less than 0.3 percent from 20 to 20,000 cycles per second at full output. That distortion figure came from a single period source and has not been independently corroborated. Treat it as the spec McIntosh and its reviewers were quoting at the time, not a lab-verified number.
The manual confirms the architecture: 75 watts per channel into 4, 8, or 16 ohm loads in stereo, or 150 watts mono into 2, 4, or 8 ohms. The amplifier uses four KT88 or 6550 output tubes, three 12AX7A input and phase-inverter tubes, and four 12AT7 voltage-amplifier and driver tubes. The output transformer windings are part of the Unity Coupled Circuit itself. There are two bifilar-wound primaries, one for the cathodes and one for the plates, with the secondary wound together with them. That close primary-to-secondary coupling gives the MC-275 its flat frequency response and wide power bandwidth. It's also why the output tubes run cooler than the tubes in most of its contemporaries.
The MC-275 is the most revered McIntosh tube amplifier. It has been in production on and off for decades, and the modern version is now in its sixth generation. The original hardwired edition remains the one purists chase. It's the most powerful of the vintage Mac tube amps, and arguably the most coveted.
Key Features
Unity Coupled Circuit with Bifilar-Wound Output Transformer
The Unity Coupled Circuit is McIntosh's patent, and it drives the whole design. The output transformer uses two bifilar-wound primaries, one for the cathodes and one for the plates, with the secondary wound alongside them. This gives very close primary-to-secondary coupling, and according to McIntosh's own documentation the result is flat frequency response and wide power bandwidth. The circuit also runs the output tubes cooler than conventional designs, which helps with a quartet of KT88s idling under a chassis.
75 Watts per Channel, Stereo or Mono Parallel
In stereo, the MC-275 delivers 75 watts per channel into 4, 8, or 16 ohm loads. In mono parallel it produces 150 watts into 2, 4, or 8 ohms. The rated power band is 20Hz to 20,000Hz, with total harmonic distortion specified at a maximum of 0.5 percent at any power level from 250 milliwatts to rated output. Intermodulation distortion is also 0.5 percent maximum, provided the instantaneous peak output per channel doesn't exceed twice the rated output. Two custom gold-plated jumper bars were included to make the mono parallel connection easier and to maximize power transfer at the output binding posts.
Balanced and Unbalanced Inputs
The MC-275 accepts both balanced and unbalanced sources. Input impedance is 100,000 ohms unbalanced and 200,000 ohms balanced in most manual versions, though one service document lists 90,000 and 180,000 ohms respectively. Sensitivity is 1.2 volts for unbalanced inputs and 2.5 volts for balanced, though one service document lists 1.0V to 30 volts through the gain control unbalanced and 2.0 volts fixed balanced. The balanced connections guard against induced noise and allow long cable runs without compromising sound quality, which helps when the amp sits at a distance from the preamp.
Sentry Monitor Tube Protection
McIntosh's Sentry Monitor circuit protects the output tubes and ensures the amplifier has a long, trouble-free operating life. It's one of those features you never notice until it saves you a set of KT88s, and it's part of why so many original MC-275s are still running today.
Gold-Plated Connectors and Ceramic Tube Sockets
The input jacks and output binding posts are gold-plated for trouble-free connections. The tube sockets are ceramic with gold-plated contacts, which provides protection from atmospheric contamination. The output tube sockets include Air-Pipe cooling at their bases.
Super Mirror Chassis Finish
The MC-275 uses McIntosh's stainless steel chassis with the company's Super Mirror finish. The finish is designed to retain its appearance for many years. The modern sixth-generation version is nearly identical in appearance to the original, though underneath, almost everything else has changed to varying degrees.
Historical Context
By 1965, the MC-275 was the stereo power amplifier McIntosh was listing at the top of its lineup. It appeared in the company's period advertising alongside the C22 preamp, the MR71 tuner, and the MA230 compact preamp-amplifier, as the "MC 275 stereo power amp" in a full-page spread that ran in Audio (May 1965, p.43). That same year, High Fidelity (December 1965, p.156) gave it the "Stereo Power House" description that stuck.
The amplifier stayed on the market a long time. Two decades after it first appeared, a classified listing in Audio (November 1985, p.118) still had the MC275 in dealer stock, offered alongside McIntosh power amps like the MC60, MC225, and MC240 - more than forty pieces of McIntosh in a single shop. McIntosh has brought the MC-275 back multiple times since.
Collectibility & Value
The MC-275 is the most revered McIntosh tube amplifier, and the market reflects that. Used examples turn up on 400-plus second-hand hi-fi sites and shops, and listings regularly appear on Audiogon and similar venues, including MK III and MK-V versions described as mint and complete. No confirmed current market prices for the amplifier itself were found in the Archive's research. Asking prices vary widely with generation, condition, and whether the unit has been restored.
The original hardwired edition is the one collectors chase. The maintenance picture is straightforward: a "Power Supply Capacitor Restory Kit" for the MC-275 exists as a sold product at around $299, which implies capacitor restoration is a known activity for these amplifiers. Tube sets are also available from parts suppliers. No owner complaints or common failures beyond the implied capacitor work were found in the research, but anyone buying a sixty-year-old tube amplifier should expect to budget for tubes and capacitors.
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