hi
i would solve the noise issues by a tech and than replace both 12au7 at least. china is the worst source for any audio gear ide wait till i can afford it and go only with nos nib guaranteed (the older the better). i have experience with a few great nos 12au7 tubes these are my favourites :
1.mullard 10m goldpin 12au7 :the end of tube rolling,the cleanest tube with the widest stage and frequency extension the best audiophile grade preamp tube ever made in england has a fresh hint of brightness .think if telefunkens had a soul...(if you even consider teles try amperex or simens they are sweeter sounding less dry and sound less german....)
2.mullard 12au7/12au7a 1958-1975 great low mid slightly recessed highs very smooth and weighty ,healthy gain.
3.brimar warm but not smooth less bass more upper mid lots of vintage british personality ,i prefer military/industrial (12au7a /cv 4003)versions since they have a lower noise floor (it's a very gainy tube)
4.ge jan military versions:well balanced sweet and crispy highs very low noise floor great clarity and definition,tames angry amps(too gainy or too sharp) .great tube and not so pricey .
5.rca 12au7a also a great tube more gain and upper midrange as opposed to the more transparent clean and hollow ge.
i would solve the noise issues by a tech and than replace both 12au7 at least. china is the worst source for any audio gear ide wait till i can afford it and go only with nos nib guaranteed (the older the better). i have experience with a few great nos 12au7 tubes these are my favourites :
1.mullard 10m goldpin 12au7 :the end of tube rolling,the cleanest tube with the widest stage and frequency extension the best audiophile grade preamp tube ever made in england has a fresh hint of brightness .think if telefunkens had a soul...(if you even consider teles try amperex or simens they are sweeter sounding less dry and sound less german....)
2.mullard 12au7/12au7a 1958-1975 great low mid slightly recessed highs very smooth and weighty ,healthy gain.
3.brimar warm but not smooth less bass more upper mid lots of vintage british personality ,i prefer military/industrial (12au7a /cv 4003)versions since they have a lower noise floor (it's a very gainy tube)
4.ge jan military versions:well balanced sweet and crispy highs very low noise floor great clarity and definition,tames angry amps(too gainy or too sharp) .great tube and not so pricey .
5.rca 12au7a also a great tube more gain and upper midrange as opposed to the more transparent clean and hollow ge.