Based on NTE1606. Powered by a12V, 10-Amp power supply. Power is 4W per channel connected to 8 ohm loudspeakers.
http://www.ee.washington.edu/conselec/Sp96/projects/rphou/final/index.htm
http://www.geocities.com/tomzi.geo/2tr_amp/2tr_amp.htm
270-Watt Double Barreled Amplifier published in Audio magazine.
http://users.ece.gatech.edu/~mleach/superamp/
The unit is powered directly from the 120 volt AC line, with no power transformers.
http://www.dogstar.dantimax.dk/tubestuf/4x4howit.htm
http://members.tripod.com/valveaudio/INFO.htm
Low distortion amplifier using discrete components.
http://www.zen22142.zen.co.uk/Circuits/Audio/2wamp.html
400 W in 4 ohms - bipolar. gives lower distortion
http://margo.student.utwente.nl/el/ampz/dpa880.html
200 W in 4 ohms - bipolar. gives lower distortion
http://margo.student.utwente.nl/el/ampz/dpa440.html