I own a Cronus and like it a lot. It is a solidly built piece that is reliable and backed by very good service.
It sounds good out of the box but can definitely be greatly improved by tube rolling and fuse upgrades. The latter adds a significant amount of resolution.
As for the tubes, the center 12AU7 is the preamp tube. The other two 12AU7s are the amp section drivers and the 12AX7s are the amp section phase splitters. The phono section does not use a tube.
For the preamp tube I prefer either NOS Raytheon black plates or the new Shuguang Pavane 12AU7. NOS Mullard CV4003/12AU7 sound wonderful as well but I've had three of them go noisy in this position. I do like this Mullard best in the driver position, however (Upscale Audio carries a driver grade level which is much less than a preamp grade one). Raytheon black plates also sound very good in the driver section.
For the phase splitters at a reasonable price, I like the new Tung Sol 12AX7/ECC803S gold pin (the regular Tung Sol might be good also but I haven't tried it yet). The best tube I've had in the position is the NOS GE 12AX7 long plate but they're expensive. I also like Japanese 12AX7s from the '70s (usu. made by Mashushita, various labels).
I find the stock Sovtek 12AX7LPS tight and forward sounding. I also find the stock driver un-resolving.
There are also better power tubes available. The SED EL34 and the Genalex re-issue KT77 for example. I prefer the Genalex KT66s (biased at 32.5 ma) and Shuguang Black Treasure 6CA7s (the latter very expensive) most of all but these require socket extenders (available here under octal socket savers: http://www.vacuumtubesinc.com/Products/SocketsAdaptersParts/AdaptersandParts.aspx).
Good listening.
It sounds good out of the box but can definitely be greatly improved by tube rolling and fuse upgrades. The latter adds a significant amount of resolution.
As for the tubes, the center 12AU7 is the preamp tube. The other two 12AU7s are the amp section drivers and the 12AX7s are the amp section phase splitters. The phono section does not use a tube.
For the preamp tube I prefer either NOS Raytheon black plates or the new Shuguang Pavane 12AU7. NOS Mullard CV4003/12AU7 sound wonderful as well but I've had three of them go noisy in this position. I do like this Mullard best in the driver position, however (Upscale Audio carries a driver grade level which is much less than a preamp grade one). Raytheon black plates also sound very good in the driver section.
For the phase splitters at a reasonable price, I like the new Tung Sol 12AX7/ECC803S gold pin (the regular Tung Sol might be good also but I haven't tried it yet). The best tube I've had in the position is the NOS GE 12AX7 long plate but they're expensive. I also like Japanese 12AX7s from the '70s (usu. made by Mashushita, various labels).
I find the stock Sovtek 12AX7LPS tight and forward sounding. I also find the stock driver un-resolving.
There are also better power tubes available. The SED EL34 and the Genalex re-issue KT77 for example. I prefer the Genalex KT66s (biased at 32.5 ma) and Shuguang Black Treasure 6CA7s (the latter very expensive) most of all but these require socket extenders (available here under octal socket savers: http://www.vacuumtubesinc.com/Products/SocketsAdaptersParts/AdaptersandParts.aspx).
Good listening.