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It took me a while to understand it. Basically, as designed, the transistor base to emitter junction And the couple and capacitor form a half wave rectifier power supply. Charging up the coupling capacitor. Until eventually the peak inverse voltage required of the basement or Junction is exceeded, and the transistor is destroyed and the coupling capacitor form a half wave rectifier power supply, driven by a strong RF signal acting like the AC input. Charging up the coupling capacitor. Until eventually the peak inverse voltage required of the base emitter junction (usually only five or six volts) ?is exceeded, and the transistor is destroyed?

Way back in the old days we were all taught how to figure out what reverse voltage capacity is needed by the diode in a half wave power supply

By adding a reverse diode across the base emitter, you stop that power supply effect. ?

Now the coupling capacitor has current moving in both directions, and can’t destroy the transistor?

Gordon

On Nov 2, 2020, at 15:26, Jerry Gaffke via <jgaffke=[email protected]> wrote:

?Gordon, I had read your argument long ago and for some reason I don't remember
this point about the C80 charging up.? Good point.

Jerry, KE7ER


On Mon, Nov 2, 2020 at 10:58 AM, Gordon Gibby wrote:

My previous discussion of the failure mode suggested that it was reverse voltage, as that coupling cap charges up. Having a reverse diode prevents that.