tube recommendation please

If the manufacturer could confirm this, that would be great, but I found a picture of your amp on the internet and it looks like the 12AX7 tubes (the pair in the front) are most likely the signal tubes and the 12AU7 tubes (the pair in the rear) are the driver tubes. The signal tubes will have the dominant sound and will be the most sensitive to tube microphonics. So, in terms of best bang for the buck, one way to look at it would be to replace the signal tubes first with the highest quality you can find, followed by the driver tubes later.

As Mofimadness mentioned, the Mullards are indeed warm and are fine tubes. If you find them too warm, RCA and Tung Sol are nice also, albeit not as warm as the Mullard.

Here's some examples of the degree to which you could fine tune your system, in order of decreasing warmth:

1. Signal & Driver both Mullard
2. Signal = Mullard; Driver = RCA or Tung Sol
3. Signal = RCA or Tung Sol; Driver = Mullard
4. Signal & Driver both RCA or Tung Sol

In my system I am currently running Telefunken for the signal tube and RCA for the driver tubes, although I am about to go all Telefunken. But Telefunken are on the neutral end of the spectrum, however, which is what I prefer.

But if you experiment with the Mullards, RCA, Tung Sol and Amperex tubes I'm confident you will find a satisfactory combination.

Gte357,

In my experience with my Rogue 99 preamp and M180 monoblocks the signal tube position, as I call it, definitely provided the dominant signature. This was also my experience with an Ayon Spirit integrated amp. It sounds like you'll have to experiment and see if the same holds true for your preamp.