Looking at these specific preamps give me your opinions

@gregjacob I replaced the 12AT7s with Telefunken ECC801s. I replaced the 12SN7s with CBS/Hytron VT-231 per a recommendation from Brent Jessee. If you use 6SN7s as a replacement, you just have to slide the internal switch in the pre to 6V. The tubes were not inexpensive, but well worth it in my opinion. The difference to me was amazing.

cbrez   Thanks for the tube suggestions!  I'll check in with Brent.  Of the tube swaps, which set do you feel made the most audible improvement?   I might try one set, then add changes from there...  Thanks.

@gregjacob I'm using the same Telefunken ECC801S.  They are the most detailed and best sounding in my system. A friend thought they were too bright in his system. The Siemens ECC801S are very good, but a hair less detailed. A fair bit less expensive, though.  The Brimar Yellow T are nice and warmer sounding if your system is already on the bright side. 

I own the PrimaLuna EVO 400’preamp. Very pleased with it. Very quiet and great sound stage. It’s a dual mono design and right at 60 lbs. A reliable preamp. 

sls883:  Thanks!  The Telefunkens might be too bright in my system but I will listen a bit to how the LTA sounds from factory, then jump for those or the Siemens, depending on the effect of the LTA pre to the overall sound.  Love detail but don't want too bright. Cheers.