The amplifier is capable of driving 4 Ohms, but it is starting to push the limits of the transistors, however, even when used at 4 Ohms, very few failures were encountered.
http://sound.westhost.com/project03.htm
If you look up in the cross reference of the ECG or NTE semiconductor manual, you will notice that the BC558 substitute will differ in the pin configuration from the stock BC558. This goes for the BC549, BC549 and the majority of the BC transistors.
http://europa.spaceports.com/~fishbake/amp/ca100.htm
P400 hi-fi high end audio power amplifier
http://www.ptt.yu/korisnici/s/r/srmarkovic/poweramp.htm
The LM3886 is the most powerful and delivers around 68 watts and peak power of 120 watts. The IC is only 20 x 15 mm and contains a whole power amplifer with 10 A output capability.
http://sjostromaudio.com/_unsql/hifi/gainclone/index.html
The LM12 is a power op amp capable of driving ±25V at ±10A while operating from ±30V supplies. The monolithic IC can deliver 80W of sine wave power into a 4 ohm load with 0.01% distortion. Power bandwidth is 60 kHz. Further, a peak dissipation capability of 800W allows it to handle reactive loads such as transducers, actuators or small motors without derating.
http://www.national.com/pf/LM/LM12CL.html
Simple 200W amplifier circuit diagram and components. Uses TDA2030 chip.
http://www.mif.pg.gda.pl/homepages/tom/files/simp200W.gif
With power supply voltages of about 58 V dc (+ and -), the amplifier will put out an average sine wave power of 120 watts per channel with an 8 ohm load. SMPTE IM distortion is typically 0.15% at clipping and less than 0.01% at lower levels. The circuit has a gain bandwidth product of about 8.5 MHz and a large signal slew rate of 60 V per microsecond.
http://users.ece.gatech.edu:80/~mleach/lowtim/
Basically, the circuit description for the Low TIM Amplifier also applies to the Double Barreled Amplifier. The major difference between the two is the addition of transistors Q22 through Q31. Q22 is connected as a common base stage at the output of Q12. The two transistors form a cascode stage.
http://users.ece.gatech.edu/~mleach/superamp/
120W power amplifier using BDX66B and BDX67B transistors.
http://xedox.de/verstaerker.html
The output devices are MJL4281A (NPN) and MJL4302A (PNP), and feature high bandwidth, excellent SOA
http://sound.westhost.com/project3a.htm