It could certainly be the tubes. 12AX7's are relatively cheap. Hopefully by now you have checked this out. Are you still having the problem?
Hum coming from my Jolida Glass FX tube DAC
I was wondering if anyone is having this problem with their Jolida DAC. Whenever I have it hooked up I get a hum noise that will not go away. I have tried different interconnects I have tried different inputs on my preamp I have tried using a cheater plug like Jolida recommended. I have everything on an isolated 20 Circuit with 10 gauge wire going into a Shunyada outlet. Everything is run through my APC H15 power conditioner also. Could a bad tube cause the hum? Any answers would be greatly appreciated thanks.