McIntosh MC240 (1960–1968)

Name: McIntosh MC240
Brand: McIntosh

Fifty-six pounds of chrome and black enamel with two 40-watt amplifiers inside. It was the last new tube design McIntosh built before transistors won.

Overview

The MC240 weighs 56 pounds net, according to the owner's manual. The chassis measures 16 1/8" × 10 1/2" × 7 7/8" and is finished in chromium and black. Inside are two complete 40-watt power amplifiers on one deck. It runs as a stereo amplifier, as a twin amplifier (two independent 40-watt channels for electronic crossover work), or as a single-channel mono amplifier rated at 80 watts. McIntosh built it in Binghamton, New York. The input switching facility makes those three modes possible, and owners can flip between stereo, twin, and mono without rewiring the back panel.

The manual is candid about the flexibility. In stereo, full rated output arrives at 2.0 volts input. Switch to the twin-amplifier input and roughly 0.4 volts will drive the amplifier to rated output, the same sensitivity the mono input uses. That matters if you run a passive preamp or a low-gain source, because the MC240 can be driven hard by components that would leave a modern power amp yawning. There are three separate gain or level controls, one per input facility, plus a balance control for the stereo channels. That is more trim than most power amplifiers of the period offered.

Power draw is quoted at 145 watts at no signal and 270 watts at full output, which says the output stage runs in class AB and idles warm. The amplifier is rated for a 105-130 volt, 50/60 cycle supply, with a line-voltage selector tapping the transformer at 117 or 125 volts. There is also a convenience outlet on the chassis good for up to 300 watts, for powering a tuner or preamplifier. That outlet is unfused.

Key Features

Two 40-Watt Amplifiers on One Chassis

The MC240 is two separate 40-watt power amplifiers on a single chassis. They share a power supply and a faceplate but otherwise operate as independent channels. In stereo the amplifier delivers 40 watts per channel. In mono, the outputs are paralleled or series-connected to produce 80 watts. The manual says that for single-channel operation the left and right outputs are combined to reach the desired impedance. It also warns plainly: do not parallel the amplifier outputs while running in stereo or twin-channel mode, because the output tubes will suffer.

Output Taps From 2 to 600 Ohms

In stereo or twin configuration, each channel offers 4, 8, and 16-ohm taps plus 25-volt and 70.7-volt distribution taps and a 600-ohm output for lines or high-impedance loads. Switch to mono and the range becomes 2, 4, 8, 16, 32, 62 (70.7-volt), and 300 ohms. The manual even includes a matching table for speakers whose voice coils don't land exactly on 4, 8, or 16 ohms. 3.2 to 6.5 ohms goes to the 4-ohm tap, 6.5 to 13 to the 8-ohm tap, and 13 to 26 to the 16-ohm tap. Most manuals of the era skipped that kind of guidance.

Unity-Coupled Output Transformers and the McIntosh Autoformer

McIntosh's exclusive high-efficiency output circuit and bifilar-wound output transformers are the core of the design, and the company's own literature treats them as the reason the amplifier exists. The Autoformer approach allows full power delivery into any of the selectable speaker loads - 4, 8, or 16 ohms - without the compromises that usually come with matching a single output tap to a range of speakers. The manual notes that the output circuit also provides low-impedance taps for direct speaker connection alongside the distribution and line-level taps. That is why the same amplifier can serve a home system and a studio or sound-reinforcement application without modification.

Tube Complement and Front-Panel Meters

The manual lists eleven tubes: three 12AX7s, two 12BH7s, two 12AU7s, and four 6L6GC or 7027A output tubes. The 6L6GC is the tube most owners end up replacing first. Front-panel power meters give a visual read on output level. The chassis is chrome with black enamel accents, the finish RetroFret documents on surviving units. A preamplifier power receptacle on the octal socket supplies 25.2 volts at 1.2 amps and 375 volts at 15 mA, so the MC240 can power a period McIntosh preamp without a separate supply.

Measured Performance

The manual's specification sheet is tight for a tube amplifier of the period. Frequency response is quoted as ±0.1 dB from 20 cps to 20 kc at full power output, ±1.0 dB from 15 cps to 60 kc at full power, and ±1.5 dB from 10 cps to 100 kc at half power. Harmonic distortion is less than 0.5% at full rated power at any frequency from 20 cps to 20 kc. Intermodulation distortion is less than 0.5% at peak power of twice the full rated output. Phase shift stays under 2 degrees from 20 cps to 20 kc, and noise and hum are better than 90 dB below rated output. Damping factor is quoted at about 10 to 1, and input impedance at 250,000 ohms across all inputs. The manual credits McIntosh's high-efficiency output circuit and bifilar transformers for reaching these numbers.

Owners and reviewers have long described the sound as rich and inviting, warm without turning soft. They single out a midrange that pulls vocals into focus and bass that stays tight, which tube amplifiers of the era often didn't manage. Highs are smooth rather than brilliant. The amplifier's reputation for driving both inefficient horns and modern high-end speakers without strain is one reason it has stayed in demand for six decades.

Historical Context

The MC240 was built from 1960 to 1968. It is generally regarded as McIntosh's first stereo amplifier and its last new tube amplifier design before the company moved to transistors. The manual describes the amplifier as suitable for "home entertainment systems and professional applications where high power and distortion-free performance is required."

Period advertising leaned on the brand's reputation rather than the MC240's specifics. McIntosh's own copy in Audio (January 1964, p.59) told readers their search was over once they'd heard McIntosh quality. It promised that patented circuits, conservative design practice, and output stages needing no bias or balance adjustment would deliver rated performance without tube matching. The same campaign ran in Audio (December 1963, p.59) and again in Audio (February 1964, p.55). That's marketing, not a verdict, but the manual's operating instructions back up the no-bias claim. They never ask the owner to bias anything.

Contemporary coverage of the MC240 comes mostly from system features rather than standalone bench tests. Audio (November 1967, p.24) ran a reader's system built around an MC240 alongside a Miracord 10H turntable, a Marantz 10B tuner, and JBL S-7 speakers. Earlier, a 1962 system featured in the same magazine paired two MC240 amplifiers with a McIntosh MR-66 tuner, C20 preamp, Crown tape decks, an Empire turntable, and Bozak B4000 Symphony speakers. All of it was mounted in a 7-foot oiled-walnut cabinet the owner nicknamed "The Coffin."

Collectibility & Value

The MC240 sits near the top of the vintage McIntosh hierarchy, and the market reflects it. Recent asking prices on eBay have run from roughly $3,300 for a unit listed as a repair project to $4,000 for a serviced and recapped example. A "late version, never serviced" unit was listed at $3,610 and a clean example at $3,700. General market value estimates put the range at $2,500 to $5,000+ depending on condition and originality, and the collectibility rating commonly assigned to the model is 9 out of 10. Condition and service history drive the spread more than anything else.

Maintenance is not optional on a 60-year-old tube amplifier. The large can-type electrolytic capacitors are the first thing to go. Recapping the power supply is standard practice whether or not the amplifier is currently working, and owners who've been through it generally recommend doing it preventively rather than waiting for a failure. The 6L6GC output tubes should be checked and replaced if noisy or weak. Potentiometers respond well to cleaning or replacement. The output transformers need particular attention. They should be tested for shorts or insulation breakdown, because they cannot be sourced new and their condition determines whether a restoration is worth undertaking at all.

Units that "power up but do not pass signal" show up in the market and should be priced accordingly. That symptom can mean anything from a dead tube to a failed transformer, and the difference in repair cost is enormous. The service manual is available as a PDF through archive.org, and a unit that comes with its owner's manual and a performance verification report is worth more than one that doesn't. The amplifier's reputation for transformation after a proper restoration is well earned, but a neglected example is a project, not a bargain. One long-time owner called the MC240 the best power amplifier they've owned, a sentiment that shows up often in owner reviews.