What are OA2 tubes and why are there more gear

using them?

I have a First Sound Presence Deluxe preamplifier which I bought used. This preamp as well as the JOULE ELECTRA use the OA2 tubes. What sort of tubes are these? When where they made and why are they not more prevalent in other preamp except in a handful of them such as the JOULE and the LAMMs, as well as the First Sound gear? What particular sound do these produce that make them appealing or unappealing for designers to incorporate them in their designs? Is there a designation that is different than the 0A2 that I am not aware off?