The C12000 stock tubes generally have a very neutral tonality - not the typical 'tube lushness' you get from the likes of Audio Research -as example, which is renowed for their 'holographic and spatial 3D imaging' - tuby sound.
However, the C12000 does respond extremely well when tubes are rolled with well chosen alternatives. This is where you need to determine what type of tube sound you prefer, and then source accordingly.
I have the following tubes in my C12000:
• 4 x Siemens E81CC ECC801S Matched Quad - Munich '68 - Same code - NOS+ (2 per channel)
• 2 x 12AX7 Telefunken / Leeds & Northrup, Tektronix, Red Tip, SELECTED TUBE label, very rare medical equipment grade smooth plate, red-tipped, diamond mark MATCHED PAIR (1 per channel)
The 12AX7 on the input stage has the first and biggest impact on the tonality you achieve in the C12000. I selected the Red Tip Telefunkens as they are extremely precise, with an ultra-low noise floor. The 2 x 12AT7/E81CC per channel is key to the final output variation of the tube sound. The Siemens tubes I chose, remain articulate, but slightly more warm than the Telefunkens, also providing a greater level of spatial imaging. If you are looking for a warmer, more lush sound, you might consider alternatives such as Mullard Bugle Boy or Amperex.
If you use the C12000 phono stage, you might consider rolling the tubes on the phono stages as well. I am currently waiting for 4 x 12AX7 Mullard LONGPLATE, medical grade "red tip" SQUARE getter, 1950s date codes, to become available for the phono stage. This will be a very warm, more analogue, 'tube lushness' before it blends with the precise imaging of the line stage tubes.
