No secret I am a fan of the 12bh7 / 12bh7a, but I recently have been toying with their less common brother, the 6gu7 which is basically a 6v version. Outstanding tall bottle tube (tall for a mini 9 pin at about 1/2" taller than say a 12au7) and can be had for a couple of bucks per tube. To note, RCA Makes a clear top version.
Maybe time to give that Sylvania 12BH7A a go again. Interesting design with the tall elements in the tube. Unfortunately no 6gu7s at my local valve dealer, but there are a couple of other 12BH7A on offer including the RCA.