Which oscillator?

On a sunny day (Sat, 18 Oct 2014 13:05:33 -0700 (PDT)) it happened snipped-for-privacy@care2.com wrote in :

So you will have to explain color codes of resistors, if they have no multimeter the part numbers of NPNs commonly used (there are a lot), the pinouts (varies), the meaning of pF, nF, uF, the strange codes used these days 103 (a 10 with 3 zeros), maximum temperature allowed with the red hot soldering nail, what is wire want is insulation, where to get a free battery... of the right voltage, many many things, that is what I mean by hand-holding.. If you can do that cool, theory MUST be present, talk about electrons, compare with water flow, although not visible gives an indication what happens or is supposed to happen.

When I was young I learned an increadible lot from van 'Aisberg's books "Zo werkt de radio" (Dutch, translated: 'That is how radio works"). Theory was good. He could teach because he knew the stuff. I see it is still for sale in various reprints

That had follow ups too, on television, on transistors perhaps? Great for kids. And even older kids, to get an idea. If you can write like that I'd buy one.

(snip)

The circuit can't drive a 1 ohm load.

& amplitude are rather low, and no tweak of R values seems to fix either - in fact most such tweaks result in oscillation failing entirely. Ditto rai sing Vcc. Drop Rout to 1k and it fails to oscillate. I'm missing something here... what?

issue fixed first.

Rout is 10k, so its driving 10k. much less and it stops oscillating. It nee ds to at least keep oscillating with any load, hence the 1 ohm test load. I t seems there's not much gain margin, as all sorts of tweaks result in osci llation failure. So I'll try the multivibrator.

NT

Gold-doped switching transistor tend to zener around 5.6V, where the temper ature coefficient of break-down voltage is about 2mV/C . If you exploit the collector-base diode as a forward diode in series with the reverse-based b ase-emitter junction you getting something very close to Motorola's 1N821

- 1N829 series of nominally 6.2V reference diodes. The zero-temperature coe fficient current isn't 7.5mA, but somewhere around a few mA.

Back in the 1960's there was a paper in the UK Journal of Scientific Instru ments (now Measurement Science and Technology) which spelled out how to use a popular gold-doped switching transistor - probably the 2N2369 - instead something out of the 1N821-9 series.

It could be this paper

--
Bill Sloman, Sydney

The battery R is 330 ohms.

Yes, so Rout is now 1K when you change it and complain. The feedback from collector back through the net into the base is insufficient to maintain oscillation when you load the collector that much.

Fine, so leave Rout high enough to continue oscillating. You have no other choice with all the other constraints you have imposed.

It seems there's not much gain margin, as all sorts of

Have played with a multivibrator, and as someone suggested its pretty much bulletproof. Just the job! Thankyou everyone.

NT

That is the million dollar question.

Why is it a question?

NT

Because I don't know if they meet all specs. If you screw up the doping what else changes.

Try a darlington for Q1 or add another 2N2222 so the emitter of the second drives the base of the first. It will drive 50 ohms but it's a little distorted and clipped at the bottom. You could lower R4 to 25 ohms and get a cleaner sine wave, but the circuit would draw 140 mA.

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I wondered about that, or adding an output stage so loading doesnt affect the osc. But once there are 2 trs, the multivibrator makes more sense.

Yes, but not compatible with running it off flat batteries found thrown out. Also would consume batteries much quicker. Everything's a tradeoff.

NT