Square wave oscillator for 50 Hertz or higher with 2 Darlingtons (4 x BD 139) Schematic and Demo

Please read the description/textbox first. An a-stabile MUVIB made with 2 Darlingtons, both of them use 2 x a BD 139. The BD 139 is a medium power transistor (Hfe/Beta = 70-150, test & try them first) that can handle (say) 3 Watt-5 Watt.

It can handle say 60 V between C-E and even 80 V on the base in a C-E figuration. Read the datasheet.

So you can use this circuit to e.g. drive a HV coil or use it as test oscillator. For that last purpose: try/test other capacitors in the 100 N-4N7 range.

Study with the oscilloscope to find usable waveforms for your electronic purpose, say needle voltages to drive a transistor/MOSFET/whatever.

A more fundamental approach (26 Aug. 2022) is here https://youtu.be/qGbHLrYFRWQ
Go to 7.44 in that video to see approx.11 different schematics of Astabile Muvibs.

The duty cycle (needle pulse time) is set with a good choice of the 2 capacitors in this a-stabile MUVIB.

Use different values for needle pulses, say 10 N (=0,01 uF non polar) or 4N7 (=0.0047 uF non polar) combined with 100 N (=0.1 uF non polar) or 470 N (=0.47 uF non polar).

Duty cycle will change substantially when the 2 capacitors differ substantially.

When a HV coil (or kind of HV coil) can only work at resonance frequency “X” for the best properties (=say HV out or whatever voltage out) adapt the frequency of the a-stabile MUVIB by changing the capacitor values and/or the 220 K resistor value and/or the supply Voltage value till you find the exact resonance frequency of the HV coil that you want to use.

On resonance the Voltage can turn up very high. Say used in old school analog TV sets, in their HV coil, that worked on 15-16/17 KC with an output voltage (on resonance on say 16 KC) 0f 20 KV-40 KV (=20000 Volt to 40000 Volt).

Often only with a few mA, say 2 mA, output DC. The wattage is then: 2 mA x 40000= 80 Watt to the (old school) television screen (=cathode ray tube), 80 Watt works good to light that cathode ray TV screen up.

This circuit is/could be usable for that application, you even can change the 3rd transistor (now a BD 139) to the 2N3055. That can work up to approx. 16 KC or 20 KC. Giving a coil its resonance peak voltage between say 10 KC-20 KC. Test/try/conclude.

Test/try/experiment or buy my books (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 25 August 2022.

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