RealityStudio.org

The letters in Rub Out The Words make it seem like tape experiments were his main thing for years. There must have been hours and hours and hours of this stuff. Does anyone know what became of the actual tapes?

There's an audio section in the Burroughs archive at NYPL. There are some 20 tapes (reel to reel) there. I think OSU and ASU have some tapes. The Estate probably has. Also Barry Miles put out a good collection a few years ago called Real English Tea Made Here. I forget where he sourced the audio for that. (Anybody have the CDs handy?) He might well have tapes himself.

Per the booklet with REAL ENGLISH TEA MADE HERE:
The tapes curated as Real English Tea Made Here were originally created in Tangier and New York in the early 1960s using reel-to-reel analogue tape, sound-on-sound technology...
Many later pieces (now lost) were recorded by Burroughs in 1965 in Paul McCartney's small experimental studio in Montagu Square, London, managed by Burroughs' friend Ian Sommerville.

..but it doesn't really say where the original tapes are currently located...

Hmm. The letters included in Rub Out discuss his own recording equipment and experiments much more than what went down at the Zapple studio. Although didn't he say that when they put the kibosh on that Sommerville took the equipment to his place?

and I would guess that the cassettes from the Norelco Carry-Corders and the Wollensacks would have been copied over to the 'proper' reel-to-reels.... and then, when the Carry Corder went DOA (p252) the static took over.... or..dare we think.. there is an attic somewhere like the one at git-le-c. ... (rats..can't find the page ref to that letter were he says he retrieved something from that attic....) ...