We found this circuit in the 1957 Raytheon transistor application manual. The transistor can be a BC558 and the common 6 V relay, just by using this voltage in the supply.
This circuit works only with carbon microphones, due its low impedance. The speaker should be good or...
This circuit produces a sinusoidal signal whose frequency can be calculated using the formula next...
This circuit was found in the 1987 Radio Electronics magazine. The components used are integrated...