We found this circuit in an old Argentine publication from the 1970s. The transistor can be the BC558 and for better performance, we can use the BF494, inverting the power, since this transistor is NPN. L2 consists of 4 turns of wire 26 or 28 in the form of 1 cm without core and the plug is made on the first or second loop. L1 is 100uH.
