About 70 years ago, E. E. "Doc" Smith wrote a series of books that are wonderful space opera: the "Lensman" series. The space battles just keep escalating throughout the series, getting more over-the-top.
My favorite plot point: they used the principles of a vacuum tube to make a device whose pieces included grids mounted in the asteroid belt, with more in other orbits closer in to the sun. In effect they turned the inner Solar System into one honking big vacuum tube, and created a weapon that could concentrate a significant fraction of the sun's output onto attacking enemy fleets. This was called the "Sunbeam". (Believe it or not, this wasn't the end of the escalation. The battles got even bigger after that.)
When you say "ultimate" vacuum tube, I think that one is pretty hard to top.
P.S. 200-word crossover fan fiction: what would have happened if the Battlestar Galactica reboot show had found Earth, and it was the Earth of the Lensman series?
When I was a teen and read those books, I just enjoyed them, but now I'm thinking that it would take a lot of trust to allow Kimball Kinnison to run around acting as judge, jury, and executioner. As readers of the books, we know that he was vetted as deeply as anyone could be by the Arisians, so he can be trusted with that kind of power; but it would be hard for the ordinary people in the world of the books to trust him that much.