Hartley oscillator help

[jpanhalt]

Here are two versions of oscillator used for model engine CDI ignitions. The similarities seem obvious.

1) Is there any reason to prefer one version over the other? I am looking for comments about factors such as efficiency, reliability, component stress, etc. that would be difficult to evaluate at home.

2) Is the diode required? Both versions will operate without it for periods up to 5 minutes. I have not tested for longer periods or under field conditons. Is there a preferred diode type for that purpose, such as Schottky?

Thanks. John

 

[audioguru]

The absolute max reverse-biased voltage rating for the emitter-base diode of a silicon transistor is 5V to 7V. It avalanches like a zener diode if the voltage is higher. The junction is tiny and is not designed to dissipate heat which happens when it avalanches. The heat slowly "eats" away the junction resulting in lower current gain for the transistor and its eventual failure.

The diode clamps the reverse emitter-base voltage to 0.7V to protect the transistor.

 

[jpanhalt]

I figured it was to prevent reverse biasing. The waveform differs depending on whether it is a Schottky or regular
(1N400X) diode. The Schottky is more regular. Unfortunately, my scope doesn't have a print feature. It seemed to me, perhaps naively, that the Schottky might be preferred for that function.

Any opinion? John

Edit: Here are the two waveforms taken at the collector of ver. B