McIntosh MC2505 Vintage Amplifier - Serviced

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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 unit was serviced in house and is ready to rock and roll.

A matching official vintage McIntosh wood cabinet is available for another $500. Please contact us if you'd like to add one to your order.

SkyFi Cosmetic Notes:

• Some bubbling around headphone jack.
• Minor glass blemishes.
• Typical light corrosion on edges of chrome chassis and tops of transformers.

Version Notes:

• The serial number of this unit is no longer legible but it's clear this is an early version. It features the large glass openings with internal meter bezels.
• Electronically this is a four trimmer unit - DC offset / Bias.

SkyFi Service Notes:

• Both multi-section capacitors were replaced with reproduction equivalents.
• All axial electrolytic capacitors were replaced due to drift that was noticed during our internal testing.
• Differential input transistors on the input boards were replaced with modern matched pairs for improved DC offset stability.
• Bias checked.
• Meters calibrated to +3dB at 50W.
• Both channels test to 50W.

Recommended Cables:

Kimber Kable - RCA Interconnects - Better 

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Speaker Cables - Better

Kimber Kable - Speaker Cables - Best

Kimber Kable - Bi-Wire Speaker Cables Best (If Applicable)

Please see our photos or the linked manual below for full specifications. 

McIntosh MC2505 Stereo Power Amplifier - Manual

The SkyFi Testing Process for Solid State Amplifiers:

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 1KHz 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 1KHz square wave check and a 20Hz to 20KHz 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. 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.