Zesto Andros II with ESP vs Modwright PH 9.0 XT?

@gakerty 

Thanks for your detailed reply.

The 12AT7 is not electrically like the 12AX7, but they will work in a socket wired for the 12AX7.  The 12AT7 will provide noticeably less gain than a 12AX7, assuming you use it in the phono input/voltage gain stage of a phono stage.  And the 12AT7 is likely to sound better with a higher plate current than what is normally used for the 12AX7, in keeping with its much higher transconductance.

I meant 12AD7 and 12DT7, not the AT7. Typo. I wouldn’t think of adding an 12AT7 in place of an 12AX7. The AD7 and DT7 are electrically identical to the 12AX7, just are considered more quiet, and were used in instrumentation and avionics. Same as the 7729 made by CBS. All are excellent, very quiet, dynamic and very wide bandwidth tubes, less "colored" than say a RCA BP 12AX7 for example.

I had a Zesto Leto Preamp.   I sent it to George for new tube sockets and the ESP upgrade while it was there .  I bought it as a demo and  believe someone whacked a tube laterally, damaging a socket.   

I can't say enough about my experience with George and Carolyn. They are some of the nicest people you will encounter in HiFi.   They could have gouged me like many companies would on a product with a $7500 price tag but parts and labor was only around $300 for the repairs.  The ESP upgrade was reasonable too and worthwhile.   

That was a phenomenal product with great support.  Only sold it to fund a DHT pre to compliment my amp.  If I could have funded that and kept the Zesto I would have..  it was the most quiet preamp I have ever owned or had first hand experience with.   Complete black background 

Thanks to all who replied.