What about Yeoman Rand's cabin then? (Seems a bit far away for his personal assistant.)
They used to be next door, but Rand caught Kirk phasering peepholes into the walls.
I copied this from my earlier notes that I referenced
at the beginning of the thread. In the notes below, there is evidence for antimatter in the nacelles and a central reactor. I try to use the least amount of Retcons to tie it all together and borrow heavily from ideas that Tin_Man, Mytran and Albertese have put forth. As always, YMMV
Personal Theory (updated with regeneration theory):
The TOS Enterprise is mainly powered by dilithium crystals that are re-charged by it's matter/antimatter reactor system containing 3 reactor cores. The central M/AM reactor core charges the dilithium crystals which generates ("regenerates") antimatter fuel and simultaneously stores energy to be used to power ship's systems through the energizers. The regenerated AM is pumped to fuel the M/AM engines in the nacelles to generate the space warp. Unused M/AM fuel in the nacelles are stored there in temporary fuel pods and excess fuel is pumped back to the main fuel areas in the engineering hull.
It can be explained that all three reactor cores aren't involved in every episode. In "That Which Survives", Losira's sabotage of the engineering hull's M/AM core was enough to have a runaway ship. In "The Savage Curtain", the "red zone" alert could be something that only can happen in the nacelles since the aliens only needed to target something
that was vulnerable.
I still can't get away from the idea that the dilithium crystals don't directly produce any energy themselves and are mainly a sort of highly important "catalyst" component that allows the engines to operate at all. All the references to the crystals being "charged" or "regenerated" either refer to the crystals' main function of producing antimatter (maybe a voltage drop required across the crystal?) or to the antimatter the crystals actually produce.