The amp is rated at 100W into a 4 Ohms load, as this is typical of a combo type amp with two 8 Ohm speakers in parallel. Alternatively, you can run the amp into a quad box (4 x 8 Ohm speakers in series parallel - see Figure 5 in Project 27b, the original article) and will get about 60 Watts.
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at
, Added: 23 Jul 2007
http://sound.westhost.com/project27.htm