In March, 1977, ETI published a very popular project called the "ETI-480", with two versions offered; a 50W and a 100W. Countless thousands of these amplifiers were built over the years. I've revamped it with a brand-new PCB layout and modern components, including the use of flat-pack transistors (as opposed to the now obsolete (and mostly faked) Motorola TO-3 transistors).

Build two of these for stereo (I would suggest a power transformer rating of at least 300VA). This will happily deliver a clean 60W into 8 ohms with little, to no problem.

NOTE 1: There is no short-circuit protection on the output, so if the output is shorted to ground, either F1 or F2 will blow.

NOTE 2: If you plan to connect a preamplifier to this/these using the same power supply and ground point, R3 the 10 ohm 0.5W resistor is to provide ground-lifting for externally connected equipment only. Connect the ground of the preamp to the GND point (or star-earth point in the chassis), not J1's "COM" connection.

Specifications:

Power output: 61W RMS (124W peak) @ 8 ohms / 105W RMS (211W peak) @ 4 ohms

Frequency Response: 20Hz-20kHz

Input sensitivity: 3.24Vp-p (1.15V RMS) for full output

Output DC-offset: <= 20mV.

Suggested uses for this: guitar amplifiers, home audio power amplifiers

ERRATA:

It has been found that the two 33 ohm resistors need to be 1W devices (or they will smoke at full power), and the 110 ohm resistors need to be at least 1W - 2W, as they will get hot as well. There is enough space on the PCB to accommodate these larger devices if you bend the 0.47 ohm 5W resistors towards the output transistors. Alternatively, you could mount these large devices on the underside of the PCB. The 33 ohm 1W resistors will still get quite hot at full power, so make sure to keep it as far as possible away from RV1 (bias trimpot).

Link to the video about this project, including detailed construction tips, especially how to attach it to a heatsink: