Radio Sofia, as it was called in my youth, was another prized East European station that radiated well into the western United States back in the late 1960s and early 1970s. I was never so much interested in their programming, rather it was their QSL card, and this I obtained at least once or twice before I stopped listening to short-wave broadcasts altogether.
When I picked up the radio again -- a Panasonic RF-B45 -- I tuned into a re-branded station -- Radio Bulgaria International. Often I would listen to their English and German language broadcasts, and catch some very nice music!!! I would usually follow up with a reception report to collect their QSL series of houses and landmarks around Bulgaria, which they promptly provided until their short-wave closure in 2012. Along the way RBI stickers, a book on Bulgarian history and spring festival greeting was received.
After the demise of their short-wave service, Radio Bulgaria International was relayed by Shortwave Service, primarily for a European audience. Additionally, RBI offered Internet broadcasts, which personally never appealed to me.
Presently, Spaceline Ltd Bulgaria is the only broadcaster from Bulgaria. It relays various transmissions from its Kostinbrod/Sofia. These may include broadcasts by Voice of the Week, The Mighty KBC, The Isle of Music, Voice of the Report of the Week, Bible Voice Broadcasting, The Overcomer Ministry and ESAT and many others.