Wow, there is more air floating around Altec A7.
The strength of Melz 1578 is deep and impactful bass, wide and deep soundstage with pure but slightly less treble.
While my Chord Dave Dac sent to AS center for repair, I had been using EMMLab Dac2 which give more organic and impactful sound than Dave.
Dave and Mscaler combo give more details and pinpoint imaging in 3d space.
With Dave and Mscaler and Lansche 4.1, I prefer Melz 1578 to other 6sn7 tubes made in USA.
But with EmmLab Dac2 and Altec A7, I prefer RCA vt231 to Melz 1578.
I may switch back to TS bgrp 2 weeks later.
Although I have 3 pairs of RCA vt231, I have only one pair of TS bgrp which is damm expensive for small input tube.
It is kind of mix and match.
There are no best tubes for everyone.
Vintage audio tubes are like vintage wines.
As some people collect lot of varius wines, I collect vintage tubes.
You may choose a tube depending on system and your mood.