07-15-10: Grimace
Right, but to the best of my knowledge, the Nevistors are only in the pre section of the integrated, not the output power amp section.
Should the adjustment have any practical effect on sound?
you usually do not bias the preamp tubes (I cannot think of one tube preamp that gives the end-user the option of tweaking the tube bias. Someone do correct me if I am wrong). It is the power tubes in a tube power amplifier that have their bias adjusted by the end user. The reason that this is done is because bias on a (power) vacuum tube or a solid-state device is the key to the amplifier's sonics. No bias, no sonics & plenty of distortion.
Bias is key & each amp has it's sweet spot based on the designer's intentions. The MF Nuvista is no different.
Good to read that your amp sounds really nice after maintenance.
If your tech can teach you & if you are willing to learn, you should find out exactly how your amp is biased & which test-point you should measure (with a voltmeter) to ascertain the bias. Bias of an amplifier can drift over several months hence it might be a good idea to simply do a bias check every 6 months & ensure that the bias is where you'd like it to be or where the manuf suggests it be.