I've been using a Calypso for a little over a year now. With the original tubes, the preamp sounded too thin and solid state like. I did some tube rolling with the 12ax7's, smooth plate telefunkens and 1950's mullard long plates 12ax7 (both came from Andy @ Vintage Tube Services). I found the mullard tubes to be smoother and richer sound, more to my liking. My associated amp is a Theta Dreadnaught, with a tube amp the telefunkens might have been my tube of choice.
I also tried different tubes for the output tubes. 6922 white shield amperex and 6dj8 orange globe a frame amperex tubes. I wound up using the 6dj8's but there is not a lot of difference in the sound between the two.
In my experience, the gain tube changes the sound substantially more than the output tube with the Calypso. But like everything, all of the associated equipment imparts some sonic signature on the sound. I just like the richer sound more harmonic sound that a tube preamp brings to the system.
I also tried different tubes for the output tubes. 6922 white shield amperex and 6dj8 orange globe a frame amperex tubes. I wound up using the 6dj8's but there is not a lot of difference in the sound between the two.
In my experience, the gain tube changes the sound substantially more than the output tube with the Calypso. But like everything, all of the associated equipment imparts some sonic signature on the sound. I just like the richer sound more harmonic sound that a tube preamp brings to the system.