This amplifier for the experimenter´s bench source 1 W and uses germanium transistors but can be mounted with the pair of BD135 and BD136 silicon. For the BC107 can be used in its place the BC548. The circuit is found in an English publication of 1979. We don´t recommend using 9 V supply or batteries because consumption is something high. Changes in the 68 ohm resistor and 1k may be necessary in the case of use of modern transistors. If source is used, it must provide at least 500 mA and have excellent filtering, to prevent any snores.