Transistor Biasing Revisited

[old_coot88]

In the tread 'Video Polarity & Direct Injection' by John (vts1134), there arose some contention as to whether a resistor is needed in the emitter-to-ground leg of the transistor.

The argument was that the resistor is necessary to set the operating point, in the same sense that a cathode-to-ground resistor sets a tube's operating point (for Class A or linear point operation in either case).

But there's a major difference.A tube's grid is biased negative, while the transistor's base is biased positive.* Thus NO resistor is required in the emitter-to-ground leg to develop base bias. Rather, the bias is derived via a resistor from the positive supply rail.

I know this is the way I built transistor projects back in the day, all using the grounded-emitter configuration, and they all worked fine. Also, John mentioned that his circuit worked with grounded emitter right off the bat. And then the issue arose from other posters on the need for a emitter resistor.

http://www.electronics-tutorials.ws/...r-biasing.html

While refinements of the basic circuit for stability DO include a emitter resistor, that resistor isn't primarily for base bias.
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*The discussion pertains to NPN transistors. Rarely seen PNP types use negative supply voltage, hence negative base bias.