I just skimmed through this most interesting thread and thought I'd like to contribute the History of Science Museum in Oxford. Although they are currently reconfiguring the exhibition space, they still have some of the Marconi Collection in the basement, including his 1896 receiver and Dame Nellie Melba's microphone on display.
Free guided tours on Thursdays and Saturdays, and you may get me as your tour guide.
https://www.hsm.ox.ac.uk