Interesting glimpse into what was going on in Alexandra Palace in the early days:<p><a href="https://www.wondersofworldengineering.com/television.html" rel="nofollow">https://www.wondersofworldengineering.com/television.html</a><p>Unlike most such efforts, some tech details are included.<p>And this site has more than enough: <a href="https://www.earlytelevision.org/ap_black_book.html" rel="nofollow">https://www.earlytelevision.org/ap_black_book.html</a>