McIntosh MC240 Vintage Tube Amplifier with Telefunken Tubes

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Super clean and well maintained version of this classic vintage amplifier.

This MC240 is an excellent choice for a serious McIntosh collector. Beautiful cosmetics with only minor flaws, very minimal circuit modifications, and a specially selected set of period correct vintage tubes.

Electronically, this MC240 appears to be all original with the following exceptions: Select power supply capacitors were replaced, and the power cord was replaced.

The original rectifier diodes and all caps are original along with a full complement of carbon composition resistors.

Our assumption is that this amp was serviced at some point in the past, and the owner asked to only have failing components replaced in an attempt to keep the unit as original as possible.

The output tubes are all RCA 6L6GC (McIntosh branded) with matching date codes: 67-26. These tubes tested close to NOS spec and constitute two closely matched pairs.

All 12AX7 and 12AU7 are long smooth plate Telefunken. The 12BH7A are both RCA, with one showing remnants of McIntosh branding. The small signal tubes did not test as close to NOS spec as the 6L6GC, but are still within acceptable range and work perfectly in circuit.

Click below to add our recommended matching cables from Kimber Kable, all brand new as SkyFi is an official Kimber dealer.

Kimber Kable - RCA Interconnects

Kimber Kable - Speaker Cables

Please see the linked owner's manual below or our last photo for full specifications:

McIntosh MC240 Original Sales Brochure

McIntosh MC240 Owners Manual

McIntosh MC240 Schematic and Parts List

McIntosh MC240 Maintenance Manual

The SkyFi Testing Process for Tube Amplifiers:
We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and tubes are inspected for signs of stress overheating or cracking.

We then power up the unit carefully and run a simple 1k sine wave while monitoring the output on an oscilloscope for signs of distortion or noise. Finally we run the amplifier to its full rated power into the appropriate resistive load provided by our Sencore amplifier tester. If there is an issue, it will usually be noticeable at this point. If it all looks clean we will often test for THD (Total Harmonic Distortion) measured by our Keithley distortion meter, and compare it against the original manufacturers specifications. The amplifier the remains powered on to "burn in" on our test bench for a few hours to make sure there are no heat related issues. If there are balanced inputs available they will also be tested.

We also test all tubes for output gain and leakage on our calibrated modern and professional tube tester against the original manufacturers specifications. If needed, the tubes will be replaced from our vast NOS (New Old Stock) vintage or modern inventory. 

Final testing involves pushing actual music thorough the amplifier. We've learned over time that some issues are only noticeable to a trained ear while listening to familiar source material. Our test bench has reference vintage KEF speakers that we're very familiar with which quickly reveal any discrepancies. Some amplifiers will then move into our listening room where they are tested with our in-house reference speakers of choice.