This circuit was found in documentation from the 1970s. However, it can be implemented with modern transistors such as 2N2222 for Q1 and BF494 for Q2. The crystal depends on the desired frequency.
This circuit controls a heating element with voltage from 6 to 30 V and current up to 3 A from...
Indicated to operate in tube circuits, this preamplifier has 250 V power supply. The circuit is...
We found this circuit loader in a French magazine Electronique Radio Plans from July 1993. The...