I just got the the Matsu****a / National / 7DJ8 Platinum from Upscale Audio. Listening to them with my 400i. I was asked to give my impression and so I thought I would give shout out. It is hard to distinguish the sound of these compared to the stock 6BQ7. Of course they say on Upscale to give them 100 hrs burn in. So might be a little early so for that I apologize ahead of time.
It took my "Philips" (really EI) PCC88 around 30-40 hours to get it's final sound (I stopped tallying around hour 40, I guesstimate I'm round hour 80 or 90 now), or so close as makes no odds.
I agree that around $40 to $50 is the sweet spot for my wallet considering the longevity of the tube and the cost of the amp itself. I would happily reload another Philips PCC88 when this one dies, however I am quite tempted by the BEL tubes on upscale slightly above that price range though. Maybe I'll talk myself into one of those.
I agree that my upscale experience was very easy and straightforward. I'd shop there again.
Thanks for your opinion on the Matsush!ta. I was very curious about it.