Mineaturization:
The first step was to reduce the size of the glass bulb from light bulb shape to cylindrical.
The next step was to eliminate the base and to reduce the size to less than 2 inches high
After that came the sub-mineatures, about 3/8 inch diameter and less than 1-1/2 inches long, with wire leads rather than sockets (thought the leads could be cut short for use in a socket. The specification for these was that they withstand 1000 Gs of acceleration for use in 6 inch gun shell proximity fuses. They were much used in other military applications and avionics.
There were some intermediate steps, but the final step I am aware of was ceramic pill shaped tubes about the diameter of a aspirin, but thicker. These were for use in the re-entry warheads for ICBMs, as they could operate at temperatures that melted transistors.
All in all, except heat and power consumption, the vacuum tube is far superior to the transistor, able to provide 4 to 6 times the amplification per stage, handle signals at multiple frequencies (1 tube could handle the RF, IF and Audio stages of a radio in some designs). It can also do strange things, like the phantastron oscillator. This was a tube wired into the circuit all wrong that provided an extremely linear saw tooth wave, used as the time base for U.S. radar during WWII. Circuit designers added a few extra components that didn't do anything to confuse analysis should one be captured.
But, the greatest advantage for tubes is that they glow in the dark. Transistors don't to that.
The next step was to eliminate the base and to reduce the size to less than 2 inches high
After that came the sub-mineatures, about 3/8 inch diameter and less than 1-1/2 inches long, with wire leads rather than sockets (thought the leads could be cut short for use in a socket. The specification for these was that they withstand 1000 Gs of acceleration for use in 6 inch gun shell proximity fuses. They were much used in other military applications and avionics.
There were some intermediate steps, but the final step I am aware of was ceramic pill shaped tubes about the diameter of a aspirin, but thicker. These were for use in the re-entry warheads for ICBMs, as they could operate at temperatures that melted transistors.
All in all, except heat and power consumption, the vacuum tube is far superior to the transistor, able to provide 4 to 6 times the amplification per stage, handle signals at multiple frequencies (1 tube could handle the RF, IF and Audio stages of a radio in some designs). It can also do strange things, like the phantastron oscillator. This was a tube wired into the circuit all wrong that provided an extremely linear saw tooth wave, used as the time base for U.S. radar during WWII. Circuit designers added a few extra components that didn't do anything to confuse analysis should one be captured.
But, the greatest advantage for tubes is that they glow in the dark. Transistors don't to that.