Herron VTPH-2 12ax7 Recommendations?

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. 

dhcod-Good call on picking the Herron. I've had mine for about 3 years and it has served me well. When I got it, I asked Keith about tube rolling. He felt that he had selected the best available tubes that are in production. When I asked him about vintage tubes he said there were lots of options and wished me luck. I have tried Telefunkens, Bugle Boys, RCAs and GEs. I settled on GE grey plates from the 60s for all tubes but V5. I left V5 stock which I think is EI. Vintage tube aficionados will likely snicker at my GE pick. I like them because to me they sound like 60s US audio which is at the roots of my love for this hobby. YMMV but I agree with others to let the phono stage fully break in before you start rolling.