I've built this GU50 SE some time ago, using RH Universal schematics (By Alex Kitic). It sounded quite well, but I liked the 6550 version of the RHU better, so the amp went into storage, until recently...
Recently I pulled it out of storage, and decided to try a triode-strapped GU50, along with some additional mods to the PSU. As a triode, GU50 is a more "difficult" tube to work with, though, and needed a different schematics. After some research and experimentation, I ended up with a SRPP front end and fixed bias for the output tubes...
Anyway, the initial impressions are quite good: tight and crisp bass, lovely mids; highs are good too. The sound stage is not as wide as I remember it the tubes in pentode mode, so I think the amp still could be tweaked a bit more.
The GU50s are biased at 100mA, I did not hear significant difference in sound until I went down to under 70mA; B+ is at 420V. I ran the GU50 at 120mA each for about an hour with no visible/sound problems. The PT and OPTs were made by Heyboyer.
Anyways, just wanted to share ... Once the amp settles in, I want to take some measurements, and then try pentode as a driver (thinking Russian 6J52P).
Thanks, Paul.
Recently I pulled it out of storage, and decided to try a triode-strapped GU50, along with some additional mods to the PSU. As a triode, GU50 is a more "difficult" tube to work with, though, and needed a different schematics. After some research and experimentation, I ended up with a SRPP front end and fixed bias for the output tubes...
Anyway, the initial impressions are quite good: tight and crisp bass, lovely mids; highs are good too. The sound stage is not as wide as I remember it the tubes in pentode mode, so I think the amp still could be tweaked a bit more.
The GU50s are biased at 100mA, I did not hear significant difference in sound until I went down to under 70mA; B+ is at 420V. I ran the GU50 at 120mA each for about an hour with no visible/sound problems. The PT and OPTs were made by Heyboyer.
Anyways, just wanted to share ... Once the amp settles in, I want to take some measurements, and then try pentode as a driver (thinking Russian 6J52P).
Thanks, Paul.