I don’t know where this nonsense about 6DJ8, E88CC’s not working in the BHK PreAmp came from. The amp is designed for them and they work fine. I have used many of these over the years with excellent results. Some can be noisy and those should be disregarded. Not all tubes are equal. Many supposed NOS are actually “Pulls” from old equipment. They may have many hours on them or none. Invest in a Tube Tester and you’re covered. I paid $150 Canadian for my B&K Dyna 606 and it’s like new and has saved my butt many times. My favorites after 3 years with the BHK Preamp are the Telefunken 6DJ8’s.
Simple, the 12au7 is inherently a much better and tighter spec’ed tube than a 6dj8. That’s why you see it in great $10k pre’s and phono pre’s.
Whenever I mention 6dj8s to amp repairmen and amp designers, curse words fly out of their mouths. They are way too hit and miss. And the quality runs the gamut. I am sure that’s what led to having to develop 6922 and 7308s. I have 30 years with that tube and I have seen pre’s that simply will not turn on with them, but they test fine. I spend more time on a Hickok 539b testing, matching 6dj8/7308s than any other tube. Why do you think ARC and Sonic Frontiers used Sovtek 6922 in the 1990s? They sounded MEH but were tightly spec’ed and internally matched. They worked and lasted forever.
There are a ton of great nos 12au7s out there, even some new ones are OK. And you can concentrate on sound, not whether if the amp will turn on.
Once I changed the voltage they were fine and not noisy. I just found them a little more brittle than the gold lions I usually use. However, I like warmer sounding equipment so maybe just not for me. Was worth a try.