The transformer primary values were arrived at by disregarding the common values used, which are really just general recommendations, and actually measuring what the tube responds to in circuit. This is where the tube's power/distortion ratio are optimised. On either side of this point either the power falls off or the distortion goes up. Jack Elliano brought this up while we were discussing the design of the output transformers. In the case of the 6C45 this point turned out to be 3.3K and it correlated with earlier listening tests with a "stock value" transformers using different taps. I have found that common transformer primary values err on the side of less distortion and although this is theoretically appealing and measures well for less "total harmonic distortion" it is often not the best sounding loading point. Sonics at the intersection described above are what worked best with this tube in this circuit. Here there is the most "life" in the music and things breath better - unrestrained. I would guess harmonic ratios might be optimized here. Playing with the various taps on commercial amplifiers often yields better sounding results than the manufacturers recommendations. With multiple output taps the customer might find an effective tube loading that the designer didn't try because it did not measure as well in some particular test. The same measurement can be taken with any amplifier and the optimized speaker load for it discovered. When someone asks me how much "total harmonic distortion" an amplifier has I can only reply: "how much would you like"? All devices have distortions, an optimum ratio these is often of greater significance than the total amount. This is why "near perfect" transistor amplifiers, which measure so well in certain tests, can cause listener fatigue quite rapidly and bring little joy. Music is intricate and basic measurements or electronics mathematics do not reveal its secrets. In the case of the Tortilla I am balancing power and distortion while accepting a poorer THD figure for a more natural sound. With better instruments, such as a distortion analyzer, the harmonic spectra can be seen and the more natural sounding ratios better understood, however, the ear can always be used...
AZZOLINA AUDIO SOUND MATTERS