Please read the description/textbox first. This is a demo of a quite powerful audio beeper (also usable for ultrasound) working on 1 battery of 1.5 Volt.
You can also use 2 batteries of 1.5 Volt in series, so together 3 Volt. Output level does not change much.
Frequency could/will be somewhat higher on 3 Volts, anyway. More or less everything is told in the video. Real audible audio level that can be heard in practice depends on the quality (price) of the loudspeaker. A normal (not a ceramic) tweeter of 4-8 Ohm made to reproduce 8 KC-22 KC gives the best results.
The very peculiar and rare thing is that the circuit needs a “reversed” PNP transistor (BD 140) and with reversed I mean: that PNP transistor is not connected to the circuit in the normal way.
So it has its emitter on (-) instead of the + positive. I tested the circuit over and over, reversed that transistor, test-soldered it into in a so called “proper” way, did many experiments, but nothing functioned better than this.
So I publish the circuit “as it is”. It works.
And in the 1980s or 1990s the “Elektuur” Magazine in the Netherlands has payed attention to this phenomenon of mounting transistors in a reversed way and all their effects on proper or not proper or bad & fainting properties. Normally this never works, but sometimes there is some (..!?) effect. It completely depends on the electronic circuit where that transistor is used/switched in.
I am sure also in the US and the UK there were these publications in the past, discussing this issue.
The strange thing is that sometimes this reversed mounting of a normal Silicon or Germanium transistor can help or make an electronic circuit work. Not in its normal way, by the way, say acting as an amplifier or amplifying current. Say due to their so called "negative resistance", that means that they (can) effect in a certain way opposite to Ohms Law.
But e.g. (thus) using their diode effect and/or where they started to work as (sawtooth wave) oscillators. Of course such a 1 transistor (reversed) circuit has a very low level output (AC) voltage and a very high output impedance. Making it not easy to take an AC signal out. Anyway, a FET can be used.
There is 1 video on my YT Channel where I also show that effect. Also in one of my books I have used a reversed (normal) Si transistor as a “trigger” in an oscilloscope circuit. Giving it pulses on its transistor base, the Collector-Emitter breaks down (like a Thyristor), driving the High Voltage transistor (responsible for the horizontal time base/triggering the dot on the screen) to make the studied waveform stay stable on the oscilloscope screen.
Told in my book “Schematics 3, transistor switches, generators and cathode ray tube circuits”, page 44, available on the LULU website, author Ko Tilman.
My You Tube channel trailer is here: https://youtu.be/xbgQ8T3oqh4 When you search, search always “NEWEST FIRST” to get the right overview. You can also search via the “looking glass” on my Channel trailer via keywords like ”audio”, “radio”, “amplifier”, “filter”, “Shortwave”, “transistor”, “FET”, “oscillator”, “generator”, “switch”, “schmitt trigger” etc; so the electronic subject you are interested in. My books about electronics & analog radio technology are available via the website of "LULU”, search for author “Ko Tilman” there.
https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=Ko+Tilman
I keep all my YT videos constant actual, so the original video’s with the most recent information are always on YouTube. Search there, and avoid my circuits that are republished, re-arranged, re-edited on other websites, giving not probable re-wiring, etc. 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 4 June 2022.