McIntosh MC-2100/MC-2105 Power Amplifiers
These two power amps are considered together because they are the
same internally, with identical repair considerations. The difference
is that the 2105 is the dolled-up version. It has the glass front
panel, the blue meters, and if you're lucky, the wood case. The 2105
set the standard for most of the later Mac amps for appearance. The
2100 is the utility version. It sits on the chassis used for MC-240,
and is rather industrial looking. That certainly doesn't mean that it
is ugly, it still has the black transformer covers and the chrome deck,
it just doesn't have those pretty meters.
The usual 2105/2100 in for repair needs a good cleanup, as always.
It is also a good idea to see to it that the screws on the filter caps
are tight. Likewise, the screws holding the output transistors to the
heat sinks will frequently loosen up slightly over years of use, so
tighten these a bit. While you're at that, scope out the numbers on
the output devices to see that they all are Mac numbers and that they
all match. Less than qualified technician wannabees will sometimes
deal with amp failure by throwing in all sorts of non appropriate
parts. Using original Mac numbers enhances both performance and
reliability. Both of the driver boards are secured to the heat sinks
and are plugged into multi-plugs mounted in the chassis. These are
usually in good shape, but it is always possible that some bozo has
broken the plug in. It is a good idea to buff off the pc board lands
which actually go into the plug in and spray a bit of cleaner into the
plug itself. On the pc board, you will want to automatically replace
the differential amp transistors. Get these from McIntosh. Also, one
of the driver transistors on the driver board makes its collector
connection to the board through a screw. These get a bit of corrosion
under that screw head. Take the screw out, and dremel the whole area
with the little wire brush, and it will contact much better. When all
of these things are done, most 2105/2100 amps will work well. When
you burn it in, note that the heat sinks on both channels do not warm
up much. These guys do not run hot when they are set up right, in
fact, they can easily sit in a set up which requires that they be
powered on all of the time.
When you have done all of the above, you are mostly done. The
capacitors in these are often ok, but look them over carefully just to
be sure. The transformers, either output or supply, never go out. If
someone tells you that the transformer is bad, assume until proven
otherwise, that he is either incompetent or trying for some nefarious
reason to fool you. Before reassembly, you want to check the light
bulbs behind the front panel of the 2105 and either replace them all
or at least the dead ones. There are no lamps on the 2100. Lastly,
be damn careful when reinstalling the glass front panel on the 2105.
These will not take any stress and will crack big time with one false
move on your part. The glass panels can be had from McIntosh, but they
are way too expensive to be breaking them just by being careless.
McIntosh rates these amps at 105 watts rms/channel. They will
always beat that. When set up properly, they will do a fine job on any
number of speaker systems. They sound solid and authoritative. I
have always enjoyed using them.
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