The purpose of this circuit is to amplify the signal of a phone pickup and to be able to reproduce the conversation on a speaker and everyone can hear. The circuit is a publication of 1979, but can be mounted with the BC549, BD135 and BD136 in place of the original. Power should come from a source with at least 500 mA. The pickup coil L1 is formed with at least 200 turns of wire coil and positioned adjacent to the telephone, by selecting the position which gives the best results. This circuit works only with phones whose headset is of the magnetic type. The output transistors must be provided with small heatsinks and power supply must have excellent filtration.
