My background is in electronics. I'm a test system design engineer for one of the largest international manufacturing companies in New Zealand. Our product line is mostly electric fence energizers, but we are also world leaders in farming scales and milk meters. A new venture is developing a brain activity monitor for premature babies. I'm also one of the top paid engineer here. I've started in electronics 18 years ago. Was never interested in house wiring.

With a traditional kettering ignition, a magnetic field is built up in the primary. When the CB opens, the energy has to go somewhere and gets transfered to the secondary. The condencer is there to provide a low impediance return path for when the spark occurs at the plug. The output voltage is a function of the circuit impediance.

With CD, the energy is stored in a storage capacitor, and the coil output voltage to stored voltage has a similar ratio as the secondary winding to primary winding ration. The coil is purely a stepup transformer. The spark occurs when the coil primary is connected to the storage capacitor (in kettering it is when the primary is DIS-connected from the supply).

Sorry, my mistake about the location of the resistor. I was at work recovering from a cold, and typed faster than I was thinking. The resistor is to protect the coil by limiting the maximum primary side current, and is also part of the reason why the magnetic field builds up slowly in the kettering ignition. With kettering you can get multiple sparks even at high revs, but the sparks are not that strong. There is little energy in the spark. With CD you can get high energy in every one of the multiple sparks, because a capacitor can charge up very fast.

As said, I do not know how Pertronix works and was guessing. Based on what you say, I still recon there is a transistor somewhere, because that type of sensor can not normally drive the required current. Even if it is only a single transistor in darlington pair configuration with no other components, but it will still classify as transistor assisted. By the way, dwell time is only relevant to kettering ignitions, because the primary side of the coil needs time to build up a magnetic field to store energy before the ignition event, when the energy is transfered to the secondary. With CD, there is no need for dwell time as the storage capacitor is continiously charged up waiting for the next event. CD works exactly the same as virtually all properly designed electric fence energizers.

A spark is a short circuit. When a spark occurs, there is virtually no electrical resistance to the flow of current, which is defined as a short circuit. The fact that it is through air (fuel mixture) instead of wire has nothing to do with the fact that it is defined as a short circuit.

So Clayton, what is your background in electronics?