6h30 tube

I'd give 6n6p tube a try. I use them in my BAT preamp with excellent result.

They made a difference when I tried them in a CJ Act pre, they were worth the money to me.

This subject has been addressed several times in the archives. IME, NOS DR sounds better in VK75SE, but after 1200 hrs. an aged DR is surpassed by a fresh EH or Sovtek. There are relatively simple & inexpensive mods that can be done inside chassis to greater effect than DR tubes.