General:The MC2505 can provide a nice clean 50W per side, perfect for getting the most out of your high-efficiency speakers. Featuring that signature vintage warm & sweet McIntosh sound as you would expect from other models from this era. Plus gorgeous traditional blue meters like most desirable McIntosh amplifiers.We were playing period-correct hits from Frank Sinatra and I was personally mesmerized at the spaciousness of his voice against the orchestra with this amp. Even at low volume.This MC2505 is not in perfect cosmetic condition, but is functioning well and ready for many more hours of music playback.SkyFi Cosmetic Notes:This MC2505 came to us in rough cosmetic condition but we made it look great. The chassis has some light oxidation but the transformers and meter cover have all been painted black and no longer have their stickers. The glass was replaced at some point in the past with a clean piece. This is a very early version of the MC2505 with angled meter bezels. The replacement glass is the new style with a small viewing window.SkyFi Technical Notes:This amplifier is currently functioning as designed. It was serviced in the past which was evident by some replaced transistors on the driver boards and newer electrolytic capacitors on the input board. The age of the replacement parts suggests the last service took place around the 1990's. We cleaned the controls, calibrated the meters, and checked both amplifier channels for proper performance.Brand Background:McIntosh Laboratory is an American manufacturer of handcrafted high-end audio equipment based in Binghamton, New York. The company was founded in 1949 by Frank McIntosh. The company designs and produces audio amplifiers, stereo tuners and other consumer electronics products.Ownership:Single OwnerConnections:RCA input, AC power outlet,General Sound:Smooth, uncolored, undistorted natural and cleanCosmetic Condition:5/10 = Average. Multiple scratches, including some on the front faceplate. See our detailed rating description here.Working Condition:Working perfectly and tested in our lab and listening room.Included:Just the UnitPacking:Will be packed using our highly developed in-house process and custom packing materials.Specs:Power output: 50 watts per channel into 8Ω (stereo)Frequency response: 20 Hz to 20 kHzTotal harmonic distortion: 0.25%Damping factor: 10Input sensitivity: 0.5VSignal to noise ratio: 90 dBSpeaker load impedance: 4Ω to 16ΩDimensions:Size: 5-7/16"H, 16"W and 13"DWeight:38 lbs.Approximate Age:1967Link to Manual:Click HereRecommended Cables:Kimber Kable - RCA Interconnects - BetterKimber Kable - RCA Interconnects - BestKimber Kable - Speaker Cables - BetterKimber Summit Series Monocle XL Speaker Cables (PAIR) - BestTesting Process:We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.If the amplifier passes visual inspection, we move on to a controlled power on sequence using a Sencore safety analyzer to monitor current draw in real time. Once the amplifier is determined to be safe to operate, we connect it to full AC mains for function and power testing. We connect the speaker outputs of the amplifier to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1 KHz test signal at the amplifier's input and slowly increase its amplitude while monitoring the output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. If the device under test has both balanced and single ended inputs they are both tested at this time.We finish off the bench evaluation with a 1 KHz square wave check and a 20 Hz to 20 KHz sine sweep to assess the amplifier's frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours minimum. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature.
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