If you are looking for free online access to printed material about old-time radio, let me recommend AmericanRadioHistory.com. The site contains a seemingly endless supply of magazines, yearbooks and other printed matter related to various aspects of radio — programs, people, the business side, technical stuff, etc.
Some material is more recent than the OTR era, but the site has enough of the latter to make for good research and/or enjoyable browsing. The material isn’t limited to radio, either. If you are interested in TV or recording, you’ll find lots of publications on those topics.
Items range from periodicals such as Broadcasting, Radio Daily and Radio Mirror (in all of its title variations) to one-time publications such as those commemorating a significant anniversary of a station. The collection isn’t static, either. A “Latest Additions and Updates” page shows an almost daily influx of documents in one category or another.
If you prefer to search rather than browse, use the “Search for Text” option near the top of the home page. By default, the search engine goes through all of the site’s documents. To narrow the documents searched, uncheck the “All” box and check the boxes beside specific titles that you want searched. The default number of results per page is 10, but you can select 20, 50, or 100.
Long-time broadcast professional David Gleason is responsible for the site. He deserves much appreciation for providing a valuable resource.