McIntosh MC3500 Mk II - Black

Description

350 W Monoblock Into 2, 4, or 8 Ohms Through Unity Coupled Circuit™

Like the original MC3500, the MC3500 Mk II is a 350 W (conservatively rated) monoblock tube amplifier built around the McIntosh Unity Coupled Circuit™ output transformer — the technology McIntosh patented in 1949, and the foundation of the brand's tube amplification craft. The full rated 350 W is available into 2, 4, or 8 ohm speakers, with no compromise; a conventional tube amplifier with a single fixed tap would give up significant power on a mismatched load. Rated total harmonic distortion 0.3% max from 250 mW to rated output (< 0.20% at 1 W), 120 dB signal-to-noise below rated output, 2.4 dB dynamic headroom, damping factor greater than 25 across the audio band (Wideband). Frequency response +0/-0.5 dB from 20 Hz to 20 kHz (+0/-3 dB from 10 Hz to 70 kHz).

Eight EL509S Tubes, Similar to the Sweep Tubes of the Original MC3500

The MC3500 Mk II's output stage uses eight EL509S high-current power tubes. This tube was chosen specifically for its close similarity to the 6LQ6 — the sweep tubes used in the original MC3500. Sweep tubes like the 6LQ6 were originally designed for 1950s and 1960s cathode-ray tube televisions, where they swept the electron gun across the phosphor screen: a very power-hungry job that forced engineers to design very rugged, high-current tubes. Applying a sweep tube to audio amplification in the original MC3500 was an innovative and unconventional idea from McIntosh's engineers. By choosing the EL509S — whose cathode and heating element are particularly rugged, with a peak plate current capability in excess of 1 A — the Mk II stays as faithful as possible to the original MC3500 output design. Like the original, the Mk II also uses an additional feedback loop to enhance the linearity of the output tubes.

Fully Balanced Input Section With Three 12AX7A and One 12AT7

Like the original MC3500, the Mk II uses a fully balanced input section — three 12AX7A tubes and one 12AT7 tube with specific roles. The first 12AX7A is the differential input amp; the second is the buffer/driver for the voltage amp; the third is the voltage amp. The 12AT7 is the buffer/driver for the EL509S output tubes. All the tubes sit behind the power and output transformers, at the rear of the unit, and are protected by a 12-gauge stainless steel wire cage with a black powder-coated finish. The cage is shaped so that the patented gold-plated Solid Cinch™ speaker binding posts remain easy to access even when the cage is installed.

Power Guard Screen Grid Sensor™ (SGS) and Sentry Monitor™ Protection

The MC3500 Mk II carries Power Guard Screen Grid Sensor™ (SGS) technology — the vacuum-tube equivalent of the Power Guard® protection McIntosh uses on its solid-state amplifiers. Power Guard SGS continuously monitors the screen grid current of the EL509S output tubes; if that current becomes too high, a dedicated circuit dynamically attenuates the input signal in real time to keep the tubes operating in safe conditions, which prevents premature tube failure. The MC3500 Mk II's fully balanced input section is particularly well matched to Power Guard SGS. Fuse-less Sentry Monitor™ protection observes the output current and shuts the amplifier down if it ever exceeds safe limits — no fuse in the signal path, no associated sonic degradation.

Centered DualView™ Meter, Ergonomic Handles, and Connections

Like the original MC3500, the Mk II has a front-panel output meter — but larger and centered (instead of offset to the left) for easier reading and visual symmetry in a stereo system built around two monoblocks. It uses a variant of McIntosh's DualView™ Power Output Meter: the top scale shows output power in both watts and decibels, and the bottom scale shows the amplifier's warmup time (at power-on the needle rises slowly along the warmup scale; when it reaches 100%, it drops back to zero and the amplifier is ready to play music). The handles echo those of the original, but with a more ergonomic design that is easier on the hands when moving the 121 lb (54.9 kg) unit. One balanced XLR input and one unbalanced RCA input for connection to the preamplifier; one balanced XLR output and one unbalanced RCA output for bi-amping or tri-amping through a second amplifier. 3.5 mm Power Control ports for synchronized power sequencing with other McIntosh components.

Awards, Recommended McIntosh Devices, and Build

Awards: Sound+Image Power Amplifier of the Year 2023 (paired with the McIntosh C12000 preamplifier, the combination was named Stereo Preamplifier and Power Amplifier of the Year 2023 by Australian Hi-Fi Magazine: "the system simply sounds natural. Listen to it and you'll discover that you are listening to music — pure, simple, unadulterated music. It's not 'bright' or 'hard' or 'soft' or 'warm' or 'euphonic'… it's just as you'd expect music to sound: natural"); Stereo Sound Grand Prix 2022 Winner. Recommended McIntosh devices: the C12000 hybrid preamplifier (a pairing particularly highlighted by McIntosh and the audio press) or the C2800 reference tube preamplifier, the MCD12000 SACD/CD player, the MT10 turntable, the MR89 AM/FM tuner, the MEN220 room correction system, the MPC1500 power controller, and the ML1 Mk II or XR100 loudspeakers. Hand-assembled at the McIntosh factory in Binghamton, New York. Dimensions: 18 × 11-13/16 × 21-5/8 in. (45.7 × 30 × 54.9 cm); 121 lb (54.9 kg). 3-year limited warranty.

Common Questions

Which speaker binding post (2, 4, or 8 ohms) should I use?

Connect each speaker to the gold-plated Solid Cinch™ binding post that matches its nominal impedance as rated by the manufacturer. Thanks to the Unity Coupled Circuit™ transformer, the MC3500 Mk II delivers its full 350 W on any of these three taps with no compromise. The posts accept bare wire, banana plugs, or spade lugs. The tube protection cage is shaped so the speaker binding posts remain easy to access even when the cage is installed.

What is Power Guard Screen Grid Sensor™ (SGS)?

It is the vacuum-tube equivalent of the Power Guard® protection McIntosh uses on its solid-state amplifiers. Power Guard SGS continuously monitors the screen grid current of the EL509S output tubes; if that current becomes too high (a sign of impending overload), a dedicated circuit dynamically attenuates the input signal in real time to keep the tubes in safe operating conditions. This is preventive protection that prevents premature tube failure — useful for a high-power tube amplifier intended for long-term daily use.

How does the MC3500 Mk II's DualView™ meter work?

It is a variant of the McIntosh DualView™ meter with two stacked scales. The top scale shows output power in watts and decibels; the bottom scale shows the amplifier's warmup time. At power-on, the needle rises slowly along the warmup scale — when it reaches 100%, it drops back to zero and the amplifier is ready to play music. The meter is centered on the front panel (instead of offset to the left as on the original) for easier reading and visual symmetry in a system built around two MC3500 Mk II monoblocks.

Which McIntosh preamplifier is recommended with the MC3500 Mk II?

McIntosh recommends two natural pairings. The C12000 reference hybrid preamplifier (tube + solid-state with dedicated outputs for each): this pairing was named Stereo Preamplifier and Power Amplifier of the Year 2023 by Australian Hi-Fi Magazine, which wrote that the system "simply sounds natural." Or the C2800 reference tube preamplifier, for a 100% tube chain. Additional McIntosh devices: the MCD12000 SACD/CD player, the MT10 turntable, the MR89 AM/FM tuner, the MEN220 room correction system, the MPC1500 power controller, and the ML1 Mk II or XR100 loudspeakers for a fully McIntosh system. For a stereo system built around two MC3500 Mk II monoblocks (one per channel), the ultimate all-tube McIntosh configuration.

What's in the Box

McIntosh MC3500 Mk II 1-Channel Vacuum Tube Power Amplifier

12-gauge stainless steel wire tube protection cage

Power and preamplification tubes (pre-installed)

AC power cord

Power Control cable (3.5 mm)

Owner's manual