Mullard E188CC - but with tight bass?

I just digged into tube rolling a bit as my dac (Lab 12 Dac 1 Reference), which is using ECC88s and variants in its output stage, needs a shot of energy and atmosphere.

The stock tubes were 6922 Electro Harmonix. Well, they were okay but nothing special and lacked a precise bass. I changed over to the legendary Amperex bugle boys. My dear, that was an excellent, precise and powerful bass, but the mids were too upfront and I couldn’t relax with them.

Next one was a pair of Siemens E188CC from 1966. Excellent tube, great dynamics, but a bit too cold and lean for my taste and the bass wasn’t as good as from the bugle boys. Finally I now got some RTC E188CC from the early 70ies. Wow, that was the midrange I was missing all the time. Absolutely rich, voluptuous and full of textures. Really amazing, just like the 3D soundstage. The only thing that bothers me is the bass. Again it’s not 100 percent tight and precise enough. Maybe on par with the Siemens but not with Amperex (I have to admit I just used them for 3 days now. Maybe the burn in process will improve the bass but who knows).

So my question is - is there ANY tube out there with such an impressive rich, involving and delicate midrange like the RTC E188CC combined with a tight and precise bass like Amperex? What about the Mullard E188CC - or is it the exact same tube? Valvo, Genalex? Open to anything but I’m not looking out for a compromise regarding the midrange.
Barista, I think my Mullard RTC 7308's needed 60 hours of burnin. You should have very good bass extension by then unless something in your system is limiting the low-end.

And the heavy engineer makes a good suggestion to 
tighten up the bass.

I have the Mullard RTC 7308's as well plus the Amperex 7308's...both from the 60's.  They all sound great but the Mullards do have better bass and deeper extension.  Just keep in mind that compared to 6922's the 7308's have slightly lower gain. It has a peak gm of 11,500 micromhos where the 6922's peak at 15,700 micromhos.
I never used a 5687. Where are you using it? In something AN I'll bet.

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