The tube complement in my ST-120 is: 1960s Amperex 5AR4 Rectifier; two Siemens ECC801S (i.e., 12AT7); 1962 Mullard (Whyteleafe) CV4024 in center position; JJ Electronic KT88 (blue). As Mantha3 warns "...Tube Rolling can be addictive!" so I have a question about your impressions of various power tubes for the ST-120. A review on AudioGon regarding JJ KT88s - in a different amp, system and room set-up - indicates that JJ KT88s have good midrange but the soundstage is wide but not deep. I know that my current room set-up is not best for deep soundstage (I sit in near field and there is a large entertainment unit between the speakers) but I'm wondering if different power tubes, such as Shuguang Treasure KT88s or others, would be an improvement over the performance of JJ Blue Bottle KT88s.
Partial Review from AudioGon member:
"The JJ's first appeared dry and muted, however, after a few days they opened up, some. The JJ's exhibit a moderately strong midrange and somewhat less pronounced bass and upper frequency region. In the frequency areas where the cymbal and brass thrive, instead of a pronounced wailing of the cymbals, there was a slight burnish of the sound, somewhat subdued. The bass also felt the same way. My remarks are based mostly on a direct comparison to the Svetlana Winged C's and EH's. I can't help but to think the JJ's are made for perhaps other than home audio, like perhaps, guitar amps or something. Others talk about Class D exhibiting a certain dry sound, in my opinion; the JJ's exhibit the same. To be fair, I only have about 30 hours of use, vice 120 hours of break in. I am not sure about how much better these will get, but one thing is for sure, other tubes I have tested, sounded open and more holographic at the very beginning of use.
The soundstage, well it is odd. It seems as if the width is great, however, the sound makes me believe I am sitting close in on an ensemble versus sitting back and listening more to the music being spread out. It is as if I am sitting up close but with a wide stage in front of me. The musicians seem to be one layer deep, not to holographic. There are some spatial ques but they are not exceptional."