See if you can get Viktor to talk to Upscale or get an email from him stating the 7DJ8 is not suitable for his preamp and pursue the matter with Upscale. Did Upscale know that you planned to use the tubes in a BAT pre?
Some manufacturers advise that you can't do better than the stock tubes because that's what they designed the pre or amp with, others encourage tube rolling. I guess unless you hear from someone who has the same components and had success tube rolling, I'd follow the manufacturer's recommendations.
Some manufacturers advise that you can't do better than the stock tubes because that's what they designed the pre or amp with, others encourage tube rolling. I guess unless you hear from someone who has the same components and had success tube rolling, I'd follow the manufacturer's recommendations.