Video Polarity and Direct Injection

[Electronic M]

Originally Posted by old_coot88

It's always useful to think of a transistor as a triode analog - with the emitter the cathode, the base the grid, and the collector the plate.

Thinking of a transistor as a tube* is a really conceptually poor design approach. A BJT is completely different in behavior/operation from a tube. A tube is a voltage amplifier and a transistor is a current amplifier. Assuming DC biases are correct and can be ignored and AC analysis of a transistor looks like a relatively low resistance resistor that measures input current and controls a current source based on the current through the resistor. A tube looks like a near infinite resistance the voltage across which controls a variable voltage source.

*Except for FET transistors which are functionally and behaviorally identical to triode tubes.