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I dunno, do you have any op-amps? Making a relaxation oscillator
from op-amps is not too hard. By the way, the 555 is basically like a pre-made cake mix, for making a relaxation oscillator. Very easy to make it work. I think that's why it is so popular.
The reason I am suggesting a relaxation oscillator is that kind of oscillator is good for making square-ish waveforms. You know it has two states. When it turns on, it turns all the way on. When it turns off, it turns all the way off.
I think that's the kind of wave shape you want for your switchy-mode kind of applications. That is to say if this signal is controlling a transistor feeding current to a transformer, you want that transistor to be either, all the way on, or all the way off, with none of this in-between stuff.
I think it is going to be tricky to do this with discrete transistors, because to do this all the way, slamming from one rail to the other, requires big gains, and I don't think discrete transistors don't do big gains, or at least not as big as op-amps, or comparators.
What about this type? I know it works when designed correctly, because my 30MHz oscilloscope test output has that exact configuration, just followed with an emitter follower. I know because I have the full internal schematic, done entirely with BJT's! I also think that is the most commonly used circuit for the LED blinky kits. Gotta love LED blinkys!
Fail: I forgot to paste the link:
Oh yeah! I forgot about that one. The flip-flopping, bistable, blinky-blinky, flasher. OK. I guess I'm saying slanderous, or wrong, things about discrete transistors.
555s are very common, every electronics store has them. Anyway, you can use a relay oscillator. The good thing about 555s is you can adjust the frequency to increase the power. I don't really know how to do this with transistors, I've made some attempts with very few components but the frequency ends up being too high to use.
You can use a 555 timer! And I found them, too!
OK jokes aside, there are MANY ways you can make a DC multivibrator. You can use a relay with a feedback loop to make it oscillate, as I did with my ignition coil driver circuit 'able oscillate. https://www.instructables.com/id/super-simple-ignit...
You can use descrete transistors to make a mutivibrator circuit: https://www.google.com/search?q=multivibrator+circ...
You can use operational amplifiers to make a multivibrator oscillator circuit: https://www.google.com/search?q=discrete+multivibr...
You can use a relay to make a (really noisy) oscillator: https://www.google.com/search?q=discrete+multivibr...
Can't get that 555 where you are? Bust build your own!!! :)
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