Sophia Electric Coke-bottle KT88-ST Tubes (long-life version)
Brand new used less than 30hrs for one trade show- and tests perfect.
When I sold the Cayin 6A I kept the tubes as they are premium and worthy of the upgrade over any other KT88 I had (I had 4 sets and these were the winners)
User Experiences
This patented Sophia Electric coke-bottle KT88-ST (long life version) tube has the most refined sounding with best high frequency extension, a cure for the dark sounding KT88 amplifiers.
Alex Halberstadt's Stereophile Review:
"It was with Sophia Electric's coke-bottle-blue–glass KT88s that the amp began cooking with gas: scale became obviously bigger, separation improved, bass tightened up, and close listening became easier and more fun."
Jeff Day's Positive Feedback Online Review:
"The Sophia Electric EL34-ST vacuum tubes remind me of a cross between 45 and 2A3 triodes in terms of voicing, with a smooth, more brightly lit, nuanced, voluminous presentation of audio from music and film sources, and they are at a level above any EL34 vacuum tubes I have heard with respect to overall musicality and visuospatial performance.
The Sophia Electric KT88-ST does remind me of the voicing of a classic 300B vacuum tube, with a smooth, rich, nuanced, and voluminous presentation of music and film. The KT88-ST is darker overall than the EL34-ST, and at the same time more vivid in imaging terms.
Both the Sophia Electric KT88-ST and EL34-ST vacuum tubes shared a common trait in my audio-visual system, which is that they both produced a "bubble of acoustic immersion" that placed me into movies in a way that I felt like I was participating in the unfolding events, rather than just merely watching them, as with typical KT88 or EL34 vacuum tubes.
Regarding amplifiers, if you are the owner of an original Leben CS-600, I think the Sophia Electric EL34-ST was the best match for the CS-600's voicing. The new Leben CS-600X is considerably different in its voicing, and I found the Sophia Electric KT88-ST to be the best match for the CS-600X.
In both cases, the Sophia Electric vacuum tubes elevated the performance of the Leben integrated amplifiers beyond anything I have ever experienced from them with more typical EL34 and KT88 vacuum tubes, both in terms of musicality and visuospatial performance, and it is safe to say that the performance of these two integrated amplifiers was much higher than I thought possible when the Sophia Electric vacuum tubes were installed into their circuits.
To broaden the scope a bit to other amplifiers that don't allow for multiple choices of output tubes in their circuits like the Leben amps do, I suspect that if you have a dedicated EL34 or KT88 based amplifiers, that you will realize similar performance gains with the Sophia Electric KT88-ST and EL34-ST vacuum tubes in their circuits.
Both the Sophia Electric KT88-ST and EL34-ST vacuum tubes are easy recommendations for their stellar performance in terms of musicality, as well as their impressive visuospatial performance.
The Sophia Electric KT88-ST and EL34-ST vacuum tubes are quite a bit more expensive than more generic KT88 and EL34 vacuum tubes, but they are a classic case of you get what you pay for, in terms of musicality and visuospatial performance.
With the long operational life of the Sophia Electric KT88-ST and EL34-ST vacuum tubes in comparison to more generic vacuum tubes, the higher cost of the initial purchase will be offset somewhat over time, as more generic tubes will likely need replacing several times during that same amount of time, making the more expensive initial costs of the Sophia Electric vacuum tubes cost effective over the long term. " -- Full Review
Positive Feedback Online Reviewer Jeff Day:
"Straight out of the boxes these KT88-ST vacuum tubes sounded rich, natural, transparent, and much better than ..." -- original article