McIntosh MC-275 mkVI Stereo Power Tube Amplifier

In Year 2011, McIntosh came out with their MC275 50th Anniversary Limited Edition which was a substantial redesign. The 50th Anniversary production run is now complete. The new Mk VI is simply a chrome plated version of the 50th Anniversary.
The differences between the McIntosh MC275 Mk V and the new MC275 Mk VI are:
• High Speed Sentry Monitor circuit will shut the amp off if speaker wires are shorted or there is a gross impedance mismatch to the connected loudspeakers.
• High Speed Sentry Monitor Circuit will indicate a failed output tube by illuminating the three small tubes Red in front of the defective pair of output tubes, greatly simplifying maintenance.
• Small tube illumination for amplifier operational status indication. The three modes are sequential: Amber on warm up, Green when amp is ready for operation, and Red if an output tube fails.
• A stereo power control cable combined with a McIntosh preamplifier allows for the small tube illumination to be turned on or off using the meter light control trim function in the preamplifier.
• Power control input and output allows one button on-off operation from the preamplifier when used in an all McIntosh system.
• Auto Off switch allows control of the new Power Save Circuitry which will switch the amplifier to Standby Mode approximately 30 minutes after there has been an absence of an audio signal.
• New Style Patented McIntosh speaker binding posts produce the very best connection with all speaker wire types and terminations.
• Higher Audio Performance Achieved. There were many subtle changes in circuits, and component values that were relatively unnoticeable by themselves, but totaled up to significantly improved performance.
In an engineering analysis, McIntosh President Charlie Randall (a former McIntosh engineer and designer of the MC352) states:
“The output transformer is the most critical component, outside of the tubes themselves, that determines the overall performance capability of the amplifier. Unique McIntosh transformer winding techniques are key to wide bandwidth and low distortion operation. The new MC275 has taken the winding process to a new level of perfection. The result is wider bandwidth and better manufacturing repeatability. Since the transformer has the lowest bandwidth of the components in the signal chain, it directly affects the overall amplifier bandwidth potential. With the new wider bandwidth output transformer in the circuit, the remaining stages can also be optimized for wider bandwidth without sacrificing overall stability. Unlike the previous MC275 series, the negative feedback is now taken directly from the speaker winding of the output transformer. This connection is made possible because of the increased output transformer bandwidth. The result is a significant increase in damping factor and deep bass definition. The main amplifying stage, the 12AT7 in V2 and V6 locations has significantly improved linearity, regardless of the individual tube characteristics or the balance between the two sections of the 12AT7 tube. Careful attention to every other circuit detail has also improved linearity with less dependence on individual tube characteristic. These small, but important details have together reduced the amount of tube thermal noise that actually reaches the speaker output.”

Specifications
Description:
Two-channel, tubed stereo (switchable to parallel mono operation) power amplifier.
Tube complement: four KT88, three 12AX7A, four 12AT7.
Inputs: 1 pair single-ended (RCA), 1 pair balanced (XLR).
Loudspeaker outputs: separate gold-plated, 5-way binding posts for 4, 8, and 16 ohms.
Preamp output: 1 pair single-ended (RCA).
Inputs: 1 pair balanced (XLR), 1 pair single-ended (RCA).
Output power: 75Wpc (18.8dBW) into 4, 8, or 16 ohms (stereo), 150W into (21.8dBW) 2, 4, or 8 ohms (mono).
Frequency response: 20Hz–20kHz, +0/–0.5dB; 10Hz–70kHz, +0/–3dB.
Signal/noise ratio: 100dB, A-weighted (no reference level given).
THD: 0.05% at any power level from 250mW to rated power output.
Input sensitivity: 1.2V unbalanced, 2.5V balanced.
Input impedance: 90k ohms unbalanced, 180k ohms balanced.
Damping factor: >14 (wideband).
Power consumption: 170W (idle), 360W (full power).

Dimensions:
16.5" (420mm) W by 8.25" (210mm) H by 12" (305mm) D.
Weight: 67 lbs (30.5kg) net, 75 lbs (34.1kg) shipping.