Please read the description/textbox first. Circuit of a Astabile Multivibrator made to work in the 15 KC-23 KC range that always works & starts. Made with a BC 547 and a BD 139. Important: the square wave is not ideally a square, anyway, very good usable.
Second video (16 june 2022) is here https://youtu.be/59E4xCl5y34
The frequency out is directly related to the supply voltage, between (say) 12 Volt and 24 Volt and the used 4N7 capacitors, say their capacitive value. That is normal, given the properties of such a Astabile multivibrator.
Correction to the video the circuit even (!) starts to work on 1 Volt....That is the absolute minimum to make a Silicon transistor work....
So the circuit is also usable for less critical electronic purposes, say all kinds of oscillators that have to work on very low voltages.
Much more info in the video. The circuit is usable to “drive” something in the ultrasound range, say a Transistor or a Darlington that drives a HV transformer.
It can also be used as function generator, when you make the 10 K resistors in the base-line to the 2 transistors (the BC 547 b and the BD 139) variable via a (or 2) potentiometer(s) of approx. 10 K.
Always (!) use a protective series resistor of 1 K from the top of the 10 K potentiometer to the (+) line to prevent a destructive base current to the transistors.
Thus: changing the 10 K resistor (s) values that go from the (+) to the base of the used transistors will change the output frequency substantially.
Again: always use a 1 K resistor as a protective series resistor to that 10 K potmeter top electrode in these cases, otherwise the transistors will directly burn out due to a too high base current when you turn that 10 K (frequency setting) potentiometer knob completely to the positive lead.
That is very important, the circuit will in that case (without that protective resistor) be defective in a fraction of a second, not giving the slightest sigh or sound (perhaps you see some smoke, at least on 24 V…).
Also changing the Cx capacitors going from collector(s) to the base(s) will surely change the output frequency, take e.g. 100 N or 50 N for an experiment. When they differ in value the pulse-pause ratio (duty cycle) will change.
That effect can be used to drive a transistor or a Darlington to its maximum (power) performance, say by driving them with needle pulses. Say (only an example): one cap is 50 N or 100 N and the other cap is 10 N.
This is not only fun and interesting, it will give you the right insight about hoe to develop electronic circuits for special applications.
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Some persons try to find gold via my circuits. I take distance from all these fake claims. I cannot help that these things happen. Upload 13 June 2022.