I always use matched tubes. Many amps allow output tubes to be biased individually but I have never seen that for smaller tubes.
Note: Tubes like the 12AU7 are stereo tubes, i.e. they each have a pair of plates, grids and cathodes. I am unfamiliar with the circuitry of the Aesthetix but many of the preamps and phono amps I have built and modified I found some tubes where half of the tube is used for one channel, the other half of the tube for the other channel. So if you are really concerned about matching tubes (like I am), make sure that the tube is matched with itself when a single tube is used as amplification stage for both channels.
I buy from a reputable dealer who always sends me matched tubes at no extra cost.
Regards
Paul
Note: Tubes like the 12AU7 are stereo tubes, i.e. they each have a pair of plates, grids and cathodes. I am unfamiliar with the circuitry of the Aesthetix but many of the preamps and phono amps I have built and modified I found some tubes where half of the tube is used for one channel, the other half of the tube for the other channel. So if you are really concerned about matching tubes (like I am), make sure that the tube is matched with itself when a single tube is used as amplification stage for both channels.
I buy from a reputable dealer who always sends me matched tubes at no extra cost.
Regards
Paul