Nagra Classic Preamp tube rolling

[Cleese74]

Hello, I am a happy owner of a Nagra Classic Preamp. Soon I will need to replace the tubes,
2x 12AX7 / ECC83
1x 12AT7 / ECC81
I don't know if buy the "official" Nagras or start the tube rolling.
Does anyone experimented with other no-Nagra tubes?

Thanks! Kind regards