E810F
Hello! I had a look at my stock list, and found that these tubes had many manufacturers in europe. Miniwatt Dario RTC Mullard Philips Siemens Telefunken It's not surprising to see some of them rebranded by RCA. In europe, many RCA manufactured types were also rebranded with local brands. It was simply a bilateral commercial agreement. E810F were often used in oscilloscopes and other industrial equipments. By the way, in pentode mode, their gain is so huge that they are strongly prone to self oscillation. Use adequate design rules, even in triode mode, to avoid such bad surprises. For audio, E180F or 6J9P (Russian version) in triode mode SRPP really give fantastic results, and are much more stable and cheaper than E810F.