Dion said:

Can you elaborate a little. Try to talk about the current. For example:

current goes down from +15V through the center tap, goes left and

down T3 and into TR1, if you can continue in this manner until you

fully describe a full cycle. This way I will know whats happening in

the electrons level, rather than talk about phase shift, inverting

configurations, and other terms which don't mean much to me.

Here is a shot. However, one of the more knowlegable folks may wish to put

forth a better description.

Capacitors are plates that are some given distance apart. They don't allow

electrons to flow across them, but act like they do; turns out that how fast

the electrons accumulate is linearly related to how quickly the voltage

changes across the plates. The constant that relates the rate of change of

voltage to the current is called the capacitance C of the capacitor.

Inductors are devices that want to maintain the flow of electrons through

them at a constant rate. If the rate of flow of electrons changes, the

voltage across the inductor will change linearly with the change. The

constant for a particular device is called the inductance L.

If an inductor and capacitor are in parallel, and a DC voltage is applied

across the two, then current (electrons) will flow through the inductor

faster and faster until the resistance of the wires limits them.

However, if an AC voltage is put across them, then an odd thing happens. One

side is increasing in voltage while the other is decreasing in voltage. If

the speed of this change (the frequency) is just right, no AC current will

flow through the inductor/capacitor combination. However, current will flow

back and forth between the capacitor and the inductor. This situation has

been compared to a spring and weight in dynamics. The AC voltage excites the

system, and the current flows back and forth like a spring moving back and

forth.

Oddly enough, however, if the AC voltage fluctuations are lower or higher

than that 'perfect' value, AC current will flow through the system. You've

probably heard of the concept of resonance. With a spring and weight, you

can 'hit' it, and it will usually oscillate at a frequency that is related

to the force in the spring and the mass of the weight. For AC, if the ac is

lower frequency, then the inductor doesn't oppose the current as much, and

the capacitor opposes it more, but the sum doesn't equal 0, so current flows

through rather than circulating. Same if its higher, although in that case

the inductor opposes the current more, and the capacitor less. Same thing,

though, the total will be less than the maximum at that 'perfect' frequency.

Set that aside for a moment.

Now, the gain of a common emitter amplifier (which is how the transistors

are hooked up in your circuit) is related to the resistance at the collector

(among other things). Larger resistance means larger gain, up to a certain

point. Resistance means the ability to block electron flow; its the same as

the AC resistance described above. Given random fluctuations, there are lots

of different frequencies in both the transistors initially. However, because

of the fact that fluctuations at the particular 'perfect' frequency are

blocked, this increases the gain of the amplifier for fluctuations at that

frequency, and decreases the gain at all other frequencies. Thus, the

natural fluctuations at that frequency are amplified into oscillations at

that frequency.

I don't usually think about these things in this way, so my descriptions are

based on half remembered physics lectures in the early 80s.

Regards,

Bob Monsen