|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|
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