Oscillator

Nope this is just filter, amplify and feedback.

Yeah, you have the positive feedback, a little voltage gain from the transformer, a little current gain from the transistor, and a frequency determining network.

http://everycircuit.com/circuit/4513027151101952

I'd also add a few peotection measures for the transistor.

Negative resistance LOL. Jason is this your newest cool slogan? This oscillator got the two basic preconditions an oscillator needs. A loop gain a little higher then 1. And second, the phase relation, lets call it phi is 0=phi mod 360. Or in other words phi is dividable by 360 without a rest! But negative resistance is just funny.

Open the oscillator loop and see how both conditions are given at 500kHz http://everycircuit.com/circuit/5152894197432320

@hurz, I see how this is a regular oscillator with the phase shift and gain, but @thebuggers version looks even more like negative resistance. In his version, as the voltage on the tank circuit rises, the voltage on the other side of the transformer rises even more causing the voltage on the emitter of the transistor to rise creating a positive voltage across the resistor putting more current into the tank circuit, and when it drops back down, so does the current, and that current going into the tank circuit at opposite of what a normal resistor would do is what negative resistance is. Right?

Which phase shift do you talking about? Zero phase shift I hope. Buggzys version??? Whats with your version?

Yeah, I’m talking about the zero phase shift. And @thebuggers version is exactly the same as mine just with a few more resistors here and there. Therefore they are equivalent.

One more reason to not escape to a different circuit

And please do not bore us of your confused idea of ​​negative resistance as the root cause of this oscillator.

In every circuit you will find a negative resistor or better said a part which behaves like one. Any power source can be seen as negative resistor. And were we have power gain as well. So better do not tell us this oscillator oscillates cuz there is negative resistance. Such oscillators exist were the dominating effect is NR, but not in this case, sorry.

Ok, I guess that almost anything can have some component or other end up functioning as a negative resistor, so I shouldn’t call this a negative resistance oscillator because it’s not oscillating only from negative resistance. I get it now.

Jason, the major difference between conventional oscillators and negative resistance oscillators is primarily the lack of an external positive feedback in the NR oscillators. They do not require a 0dgs (360dgs) feedback to ,,bump up'' the oscillations, they just need a device with such a characteristics as to cancel out the positive resistance losses in the tank circuit. Typically negative resistance oscillators are quite good. They were extensively used in the eaely vacuum tube era, to make local oscillators with a considerably good bandwidth and frequency stability. Problem was that with aging, tubes usually change their characteristics, and after a while they usually fell out of the oscillations range and the oscillator stopped working (even though the tube was still very much ok).

http://everycircuit.com/circuit/6092851011387392