This amp was acquired in the early to mid 80's.  I've used it a few times but not often over the years mainly for testing speakers and to run a second system in another room for a year or so.  It spent most of its time here on a shelf in my music room among my other cherished collectibles. A few years ago, I put it on the bench and just checked the voltages and drove it to full power while mo9nitoring the output on a scope.  It passed  the tests but I did order capacitors for it.  Recently, like in January 2016, I put it back on the bench just for the heck of it.  This time, I ran extensive tests, including total harmonic distortion tests and it came out much better than expected.  (See THD+N chart below)  It was decided to leave well enough alone based on the expression, 'If it works, don't fix it.'  I did, however, replace a lamp and spent a lot of time flushing out the front panel switches and I do mean FLUSH OUT.  These things were full of whatever it is that accumulates in switches.  I used about half a can of spray switch cleaner and a whole can of compressed air (the kind used for dusting keyboards and such)  The potentiometers were also cleaned but these weren't anywhere as dirty.

This little fella is old; the sticker on the back says,  Performance Certified  4-2-'70.  It's over 46 years old and ALL original with the exception of one lamp.  Another McIntosh testimonial.

The charts/graphs below are run with LMS, Loudspeaker Management System by LinearX.  They conform to within 2 dB of specification.  All were run with both channels simultaneously loaded with 8 ohm resistive loads.






















THD+N measured with Tektronix AA501 and PicoScope Model 2205A

The PicoScope was used as a signal source as it's distortion is far less (about 300%) than the Tektronix SG502.

The high figures at 20 hz are attributed to the old electrolytics in the power supply.  At just under 40 watts, a 20 hz sine wave is perfect on the scope but 

begins to distort as 45 watts is approached.  This amplifier is all original, another testimonial to McIntosh Laboratories.

Power (W) 20 hz 2 khz 20 khz
into 8 ohms THD +N (%) THD +N (%) THD +N (%)
resistive L ch R ch L ch R ch L ch R ch
1 (2.83V) 0.244 0.256 0.110 0.109 0.121 0.116
10 (8.94V) 0.248 0.260 0.108 0.109 0.105 0.100
45 (18.97V) 0.254 0.265 0.118 0.120 0.100 0.097





















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