I am back to Kenrad vt 231 playing "Autumn Leaves and Songbird" by Eva Cassidy.
Although 1578 Melz give best bass, decay, widest and deepest soundstage, it has two drawbacks.
The first one is slight hum and high frequency noise which is almost gone after 20 minutes warmup while KR is dead quiet without warmup.
The second one is that its treble can sound closed in slightly lacking air or sparkle.
KR vt 231 sounds very similar to 1578 but with slight more sparkle.
Thus I prefer KR to 1578 in playing lady vocal music like Eva Cassidy while I prefer 1578 in playing orchestral music.
I will take turns at tubes to taste different flavor depending on music genre and my mood.
But be sure to use socket saver if you roll tube often.
https://www.ebay.com/itm/CED-P-ST8-1000-VACUUM-TUBE-8-PIN-OCTAL-SOCKET-SAVER-for-6L6-6V6-6SN7-EL34/150688246271?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649