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McIntosh MC3500 vacuum tube amplifier, Woodstock sound in your home

Dale Davies |
There's no denying the historic significance of the 1969 Woodstock Music and Art Fair.

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That sound quality is thanks in part to the McIntosh MC3500 Vacuum Tube Amplifiers that exclusively powered the sound system used at Woodstock. The MC3500 would go on to power many other influential music events. The MC3500 Vacuum Tube Amplifier Mk II is a conservatively rated 350 Watt monoblock that takes its inspiration from the original MC3500. It has been upgraded to modern standards and with modern components to deliver an audio performance worthy of its predecessor and the legacy of their shared model numberall while adhering to the original design as much as possible.

Like the original MC3500, the MC3500 Mk II uses Unity Coupled Circuit output transformer, which allows the full 350 Watts to be safely delivered to virtually any speaker regardless if it has 2, 4 or 8-Ohm impedance. The MC3500 Mk II is powered by eight EL509S high power output vacuum tubes. The EL509S tube was chosen specifically due to it having many similar qualities and characteristics of the 6LQ6 "sweep tubes" used on the original MC3500. Like the 6LQ6, the EL509S is very rugged thanks to its robust cathode and associated heating element which produces a high peak plate current capability in excess of 1 Amp.

Like the original MC3500, the MC3500 Mk II has a fully balanced driver section that utilizes three 12AX7A and one 12AT7 vacuum tubes. 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 vacuum tubes are located behind the power and output transformers, and are covered by a 12-gauge stainless steel wire cage with a black powder coated finish. The cage is shaped so that patented Solid Cinch speaker binding posts are easily accessible even when the cage is installed.

Exclusive Power Guard Screen Grid Sensor (SGS) technology is included in the MC3500 Mk II. Power Guard SGS is designed specifically for our vacuum tube amplifiers and similar in nature to patented Power Guard technology found in our solid state amplifiers. Power Guard SGS helps prevent premature vacuum tube failure by monitoring the screen grid current in the output vacuum tubes. If the current becomes too high, a circuit in Power Guard SGS is activated which dynamically attenuates the input signal in real time to keep the vacuum tubes operating at safe levels.


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