I bought my Vac Sigma 160se after owning a more mid-tier integrated with similar tube set up. I rolled a lot of tubes in my first amp trial and error...so I had accumulated several NOS tubes . I wanted to do the same with my VAC…but it seems not much was written in this regard. So I had to experiment.
I researched what each tube’s function…through talking with Vac and AI. Vac told me V01-02 were for the phono-stage. V03&4 were for the line-stage and V05-07 were preamp tubes. They didn’t offer much advice on rolling except that they recommended V03 and V05 would most likely affect the sound the most.
AI told me….. In a line stage, 12AX7 tubes provide high-gain voltage amplification (gain factor ~100) for boosting input signals, while 12AU7 tubes operate as low-gain (gain factor ~20), high-current buffers or cathode followers, ensuring low output impedance and clean signal transfer. 12AX7s offer warm, rich tone via earlier distortion, whereas 12AU7s provide higher fidelity with more headroom and lower noise.
Looking further at the preamp stage I deducted the V05 is the driver tube. It drives the power tubes in the output stage of push-pull amplifiers. Its higher current handling allows it to "push" the power tubes effectively. The V06-07 are phase splitters. They split the input signal into two equal but opposite phases to drive push-pull amplifiers.
And of course V08-11 are the power tubes.
I should mention I am a long way from an expert on tube amps design and function. I will post what I am using in my next post