I too rolled the input tubes to Mullard for the AX7's & some French 1956 military's from La Radiotechnique for the AU7's, as suggested by Kevin Deal . The AU7's were not as important as the AX7's .
These made a huge difference in the warmth and tonality of the sound . They did not affect the great top end extension but did increase the base a bit . It also responded favorably to the EL-34's by Electro Harmonic's . The people at Upscale Audio stated that a power chord upgrade did not do much and therefore did not recommend it .
These changes increased the warmth/tonality , which is what I wanted to do . I felt that the stock tubes tended to make it sound like a SS unit . To me it is better but not generally what someone is looking for when trying to upgrade parts . For that type of better I would just change amps all together . You did not state what type of change it is that you are looking for with the upgrade .
Good Luck
These made a huge difference in the warmth and tonality of the sound . They did not affect the great top end extension but did increase the base a bit . It also responded favorably to the EL-34's by Electro Harmonic's . The people at Upscale Audio stated that a power chord upgrade did not do much and therefore did not recommend it .
These changes increased the warmth/tonality , which is what I wanted to do . I felt that the stock tubes tended to make it sound like a SS unit . To me it is better but not generally what someone is looking for when trying to upgrade parts . For that type of better I would just change amps all together . You did not state what type of change it is that you are looking for with the upgrade .
Good Luck