1) They are used for a very specific reason that doesn't relate at all to amplification technology (EMP resistance) - unless you're in a nuclear blast.
Actually, the EMP resistance is more a myth. That stuff was tested ages ago and while tubes were actually more withstanding to EMP than transistor circuits of those days many of them still failed due to it, not to mention, the equipment in general failed because the EMP toasted resistors, caps, coils, and all sorts of things. It was reasonable to say that EMP killed tube equipment just as well as it killed solid-state, the failure mechanisms just were somewhat different.
All in all, if you really want to protect stuff from EMP then you’ll be looking whole different issues than whether the active devices are tube or solid-state.
Yes, there were tubes in fighter planes, mostly in soviet ones. The reason for that was merely that their transistor technology was not on par with the western one and they could more easily get tube replacements at remote areas than transistor replacements. …Which, sort of tells that they expected that failure is indeed a serious possibility and replacement parts for repairs had to be stocked. And they had huge stocks of tubes. Another issue was that tubes, due to their enormous waste heat, did not require elaborate temperature compensations at higher and lower altitudes. Mostly, soviets just likely had to live with the fact that at those days the only thing they could work with were tubes.
Kinda like it was in the 1940’s and early 1950’s all over the world.
2) They were mostly used in digital circuits, an application which is actually less demanding by far than small signal amplification.
Never heard about the digital part and I'd wager a guess that when it comes to tubes the applications the digital stuff would be far demanding than basic linear applications. ...Or at least the world got pretty quickly rid of tube-based computers and class-D amps with tubes are likely more a total fiasco than success. So far most of the “tubes in a fighter jet” stuff revolves around the MIG-25, which as far as I know, was more of a mix of tubes AND transistor circuits. There was, for example, a voltage regulator tube in the power supply of the radio system (which today is (mis)used as an audio tube in certain applications) but rest of the radio circuitry is more or less undocumented so the entire audio part may have as well been transistor-based. In fact, that 6C33 tube is the only exact reference of somewhat generic tubes being used in a fighter plane I’ve ever heard… unless we talk about a lot older stuff.
Radars, radar jammers, target locking systems, etc. were at least somewhat tube based, and likely they still are since they are the special kind of stuff that doesn’t really have an equivalent solid-state counterpart. Needless to say, those tubes have nothing to do with audio tubes or even (supposed) EMP resistance and if you ever saw such a tube you might likely mistake it for a large motor.
Even when MIG-25 was discovered the use of tubes was sort of a miracle to western world and I doubt the soviets used them for long once they have had their transistor technology developed to a better state.
Now, if we want talk about fancy military stuff then let’s talk magamps...
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...amplifiers based on saturable cores of transformers, and which totally beat the tubes to oblivion in reliability. The navy still uses them in some radio systems of battle ships, and they were also used in avionic applications, missiles, computers, power supplies, you name it. ….And they are so obscure and vintage technology (predating even tubes) that they just must be 100 times warmer sounding than all tubes in the world together, clip so much softer than tubes and have orgasmic touch response, mostly because they generate only paranormal harmonics. And therefore one magamap watt must be equivalent to 1.21 jigatubewatts. Of course, I don’t have to substantiate any of such claims, I just believe them because some guru in Internet told me so. I think someone could also arrive to a conclusion that since military still actually uses magamps they must be resilient to both EMP and to mind-controlling laser rays of UFO’s.
Sometimes you win sometimes......
