Museum of Obsolete Media (Audio Media)
Centre for the History and Analysis of Recorded Music
See also their History of Recordings section and explore other links of the CHARM site.
Library & Archives Canada: Virtual Gramophone (Canadian Historical Recordings)
Smithsonian Exhibition: Alexander Graham Bell and the Origins of Recorded Sound
Royal College of Music (London) online exhibitions featuring historical instruments and recordings)
The Met (New York): The Art of Music Through Time Exhibition (historical instruments images and recordings of)
Personal Stereo (*navigate to p. 578* of Encyclopedia of 20th Century Technology)
For each of these, it's suggested that you follow the "see also references" or search within the same e-reference publication.
Concise Encyclopedia of American Radio
(best to click on "Read Online" at top right then search within the e-encyclopedia)
Musical instruments: history, technology and performance of instruments of Western music
Library of Congress: National Jukebox (historical recordings)
University at Buffalo Library's Retro Media: Memory (and Memories) Lost
Music Online: Smithsonian Global Sound
Not only music, but sound/soundscape recordings (see example: Leo T. Hurwitz, Here at the water's edge, a voyage in sound).