50x receivers use "Old UHF" remotes. The do NOT work with most UHF Pro remotes. 5.x remotes are IR only and would work - but only IR. UHF Pro 6.0 are IR / UHF Pro so they too would work IR (only). 8.0 are UHF Pro only (no IR) and wouldn't do anything for you.
A UHF Pro 6.2 or 6.3 remote WILL generate "Old UHF". Both in Sat mode and in Aux mode so you can use the same remote to control one 50x in Sat mode at address 1 and another in Aux mode at address 2.
You should be able to find Platinum remotes on eBay pretty cheap. 6.2's too. I had two Platinum remotes where the Sat button didn't work any longer and asked DISH to replace them. DISH sent me two UHF Pro 6.2 remotes with a little kit of plastic keys to emulate the remote of any DISH receiver (7x00 Dishplayer excluded). If you aren't having trouble with the device buttons, I have had luck opening them and cleaning them off. When the Sat button quit, I couldn't "clean it" to make it work.
A UHF Pro 6.2 or 6.3 remote WILL generate "Old UHF". Both in Sat mode and in Aux mode so you can use the same remote to control one 50x in Sat mode at address 1 and another in Aux mode at address 2.
You should be able to find Platinum remotes on eBay pretty cheap. 6.2's too. I had two Platinum remotes where the Sat button didn't work any longer and asked DISH to replace them. DISH sent me two UHF Pro 6.2 remotes with a little kit of plastic keys to emulate the remote of any DISH receiver (7x00 Dishplayer excluded). If you aren't having trouble with the device buttons, I have had luck opening them and cleaning them off. When the Sat button quit, I couldn't "clean it" to make it work.