That Phillips 5AR4GYS that’s in the Upscale link was a tube that Kevin promoted as the best rectifier tube since sliced bread. He’s definitely sales minded and promotes what HE SELLS. About 6-7 years ago I bought one of those from him that was cryo treated. I think it was about $140 delivered. I have the little Had Inspire Hot Rod 12wpc amp. I purchased some nos tubes to try. Mullard GZ 32, Mullard Coke Bottle GZ 34, RCA , RCA Coke Bottle black plate, Tung Sol and Sylvania Coke Bottle. My amp easily tolerates them all. My favorite is the Tung Sol. As mentioned Dub Girls post is great. Never got to try the exotic 274b’s however. Back then they were already too expensive for me. I don’t know squat about what your Prima Luna’s limits are but my amp responds like a guitar amp and a lower voltage rectifier tube really mellowed it out. I guess it’s the equivalent of the guitar term “ Sag “.
5ar4 rectifier tube
I’m buying some backup 5ar4’s for my primaluna evo 100 preamp. Upscale audio’s website says the Gold Lion isn’t suitable for this preamp. I like Gold Lion but there’s no explanation why. There’s only one other choice on their site. I also like Upscale audio. Advise is appreciated..