Tube replacement for the Calypso?

I think they, like Audible Illusions, went through a bad batch of the Sovteks. It happens. They test well at first and then die.
Mine made crackle noises and some hiss. It was always one tube that went bad out of the set and always the 12ax7.
A manufacturer has to use tubes that would be readily available. Hence the problem.
Since I finally got a new set of good tubes, the preamp has been absolutely quiet and produces a lovely sound comparable to the best I have ever heard.
Aesthetix always promptly replaced them without me even sending the old one back. I now have a few good spares.

That is good to know. Perhaps I should have hung in there longer.. was so frustrated I turned around and bought a nice SS pre, the Ayre K-1x. I am extremely pleased with it, but it would have been nice to have introduced tubes into my system for more roundness and warmth.

The Ayre K1x was my next choice in a preamp if I hadn't gotten the tube thing straightened out. I don't think you went wrong with it Msaines. It is truly an excellent preamp.

Has anyone tried 5751 tubes instead of 12AX7? Apparently the 5751s were developed to address the problems inherent with 12AX7 tubes.