Sometimes, people confuse about the different of transistor and tubes. This video explains the different between transistor and tube. Basically, the transistor and tube has similar function. But the construction between them is really different. This video shows the diagram of the typical triode tube. First, comparison between NPN transistor and triode tube. The label of NPN transistor is base, emitter and collector but the label of triode tube is grid, cathode and plate. The input signal for NPN transistor is the base and the input signal for triode tube is grid. The output of the NPN transistor is collector and the output of triode tube is plate. Here is the video:

Then the comparison of PNP transistor and triode tube:  the PNP transistor, the arrow is pointing up direction, the label is still same. The different between the PNP transistor and triode tube is their polarity. And big different between transistor and triode tube is, the transistor requires much less voltage to function than tube.