This circuit generates the busy tone of ordinary telephones. The transistors can be the BC548 and the components of the T filter and the multivibrator can be changed to obtain the exact tone.
Other operational amplifiers can be used in this conventional filter that rejects only one...
The integrated circuit used in this' 90s amplifier is not very common today. The supply is 24 V,...
This squelch circuit is placed at the input of the single receiver audio amplifier stage. Its...