Herron VTPH-2 12ax7 Recommendations?

Agree with stevecham, use the stock ones for a while before you start tube rolling.  Keith Herron, when he gave us a demo at an NJAS meeting, felt pretty strongly that there should be no need to change the ones he chose.  If you do decide to try different tubes, I always prefer Telefunkens, but I like their sound and their longevity.  You'll need to ask yourself what about the sound you want to change, then go from there (an excellent source for that kind of information is Andy Bouwman at Vintage Tube Services).

I've spoken with Keith about this several times and he has respectfully and gently discouraged tube rolling. He has a particular sound he is after which is achieved with the stock tubes and he is also very practical in his pursuit of hi fi so does not encourage the use of tubes that may not have the reliability of what he ships with the unit. Besides, the VTPH-2 sounds so darn good why mess?

I agree with stevecham, rcprince and dodgealum. 

I have owned both a VTPH-1mc and a [currently] VTPH-2.  I have never wanted for a different sound.  The original tubes were always very satisfying.  I'd hang with those tubes for a year or two to see how the VTPH-2 sounds to you over the long run.  That said, keep in touch with Keith Herron.  He might just find a tube combination he thinks makes a favorable difference.

Speaking of the Herron phono amp and 12AX7 tubes.....the 5751 tube is said to be a 12AX7 substitute, a military grade tube with slightly lower gain than the 12AX7. Does anyone have experience with the 5751 in a circuit designed for the 12AX7?

When I had my Octave V70SE then later the V110 I had used the RCA triple mica black plate in place of the 12ax7 input with great results. It was a warmer overall sound. Of course I did get the OK from Andreas Hoffman at Octave. He also said for those integrated amps 12au7 could be used in place of the 12at7 driver/splitter tubes which is also a lower gain.

That said I would contact the manufacturer and ask if changes like those will work. Some manufacturers design allow for flexibility while other do not.