Relaxation or blocking oscillator (HV or whatever): about their strange behaviour (demo & schematic)

Please read the description first for important info, that can elaborate the circuit.
Video about the so called “relaxation oscillator” or “blocking oscillator”.
Second video (16 june 2023) is here • Relaxation or blocking...
In the past often used in old school analog Television circuits, of course, in those days (1930’s-1940’s) made with tubes.
Much info about these old tube circuits is surely on the www, say in books on www.worldradiohistory.com.
Anyway, I made this circuit many times in the past. To make a High Voltage on frequency “X”, or to generate sounds with the help of a ferrite transformer or by using a transformer with laminated weak iron plates (originally made for 230 V/50 Hz), etc.
Key to success is the use of ferrite materials in the core/coil that has to do the job. That is the reason why I used here a ferrite transformer out of a dissected LED lamp, made for 230 V AC (can also be for 110 V AC, that does not matter). Ferrite cores work easily between frequencies of 2 KC and 50 KC. (2000 Hertz-50000 Hertz).
That tiny ferrite transformer with its double “T” core is ideal for such an experiment, but you can surely also use a standard ferrite rod of (say) 1 cm or so in diameter (length a few centimeters) to wind the all coils on (2 primary and 1 secondary HV).
Wind these coils over each other, starting with the primary windings. Here the winding named “D” is the primary coil that is switched on/off by the transistor Darlington of 2 x a BD 139.
Reason for using them: they can handle a lot of misuse and overload and the base voltage of a BD 139 is max. 80 Volt. So peak voltages coming out of the backcoupling winding (A-B) cannot easily destroy a BD 139.
Transistor properties of the used 2 x BD139: it is an NPN Silicon transistor with a current amplification of approx. 150 or 140. Thus the total current amplification in this circuit is 140 x 150= 21000.
That means that also low quality coils or coils used in a situation where the coil saturates much (or too quick) in electromagnetic terms (limiting the maximal usable oscillator frequency) also can made to work, thus: to oscillate.
Thus: also on lower frequencies, say in the 300 Hertz to 2000 Hertz range, as long as the laminated iron core of the transformer is not too big in physical terms. Say a 2 cm x 2 cm transformer with a laminated iron/steel core can be brought into oscillation with the showed circuit.
Furthermore: everything is told in the video. When you make the value of the backcoupling capacitor smaller (say 100 N = 0,1 uF, changing it to 50 N = 0,05 uF) the oscillation frequency will go up.
When you make the value of that capacitor higher (say 470 N=0,47 uF) the frequency will go down.
That can be useful when you want to get small (3x3 cm) 50Hz/60 Hz transformers with laminated weak iron cores into oscillation, say in the 300 Hertz to 900 Hertz range. The cap. must be 470 N (0,47 uF) there.
Key is to find the exact resonance frequency where such a transformer works best. These transformers are (normally) made for 50 Hertz or 60 Hertz, but often they perform better (in terms of energy transformation in an oscillator circuit) on 300 Hertz, as long as they are not too big in physical terms.
Too big (physical) means that the transistor(s) are not able to switch quick enough, due to the backcoupled electromagnetic field when they try to change the field/current.
For heavy applications: use a 2N3055 (NPN-Silicon) with an amplication factor (Hfe) of minimal 50-70 as Transistor 2, the transistor that drives the primary oscillation coil.
In such a case, remove the bicycle lamp or the 10 Ohm resistor out of the circuit, they both will hinder that a substantial current can flow into the 2N3055.
My You Tube channel trailer is here: • Radiofun232 on KZbin...
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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.
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I keep all my YT videos constant actual, so the original video’s with the most recent information are always on KZbin. 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 11 June 2023..

[@Gregi76]

Thank you very much for the very instructive video. I cannot wait for my transistors to arrive to try it out.

[@radiofun232]

You are welcome, thanks. Hope to have given you more essential info via the mail, out of that 1941 Philips Technical Review document.13 June 2023.

[@AllAmericanFiveRadio]

Interesting circuit, I’ll have to build one, thanks.

[@radiofun232]

Thanks Richard, it is a circuit that always works. If not, A & B must be reversed. But of course I don't have to tell you that......😁

[@HA7DN]

With a few iterations on this you can arrive to resonant transformer driver circuts like Baxandall's or the Mazzilli ZVS driver. In my experience these kinds of circuits can be very insensitive to a lot of factors, and I have even used them as unregulated multi-outpus PSUs, but they are the kinds of circuits that seem to be simple but getting them to work exactly how you want can take a very long time. For resonant type circuits one very important factor is the leakage inductance of the transformer. I even had early designs compleatly fail beacuse I wound the transformer too tightly coupled, and even on a later design it helped a lot when I re-wound the coils spaced further apart. For HV design, I recommend a push-pull type circuit like I mentioned above. With Baxandall's it's even easy to add some voltage feedback & regulation.

[@radiofun232]

Indeed, the crux is in what you say "getting them to work exactly how you want can take a very long time". That is also the reason why I published the circuit "as it is", used a ferrite core, and showed the waveforms on the oscilloscope (and the peculiar behaviour of this 2 transistor circuit) while turing only that 1 potentiometer. Thanks. 13 june 2023.

[@radiofun232]

With a 16 KC (old school) line transformer of an (old) analog television set, you can get to good and stable results on the basis of the circuits published in my book: "Schematics 3 - transistor switches, generators and cathode ray tube circuits", published on the LULU website. Link is in the textbox. Book nr: ISBN 978-1-4476-1164-6. Or LULU content number 10469565. Other more easier circuits are published there too, anyway thanks for your comment. The relaxation oscillator is in a kind of way "a sea to drink", also because everything that happens on the HV winding is related to the making of the circuit in practice, say because of damping and frequency issues, etc. More in my book. 13 june 2023.

[@honestlocksmith5428]

You schematics look better than mine.

[@schitlipz]

Try some nail polish on the windings to diminish the magnetoconstricion noise. (?)

[@radiofun232]

Good idea.

[@aannttoniopereira]

kzbin.info/www/bejne/mWPCo36ZbNh7fc0 ANOMALY 19:18 seconds there is an anomaly that needs explanation..

[@radiofun232]

I think the man does not understand what he is doing.