KT88 for deep bass ?

The kind of tube has little to do with how it plays bass- all tubes work to DC.
The bandwidth of the output transformer, and the way the tube matches to it is a different matter.

Just get some new production Tung-Sols. The preamp tubes have a bigger impact on the overall sound.

SHUGUANG TREASURE KT88-Z
The best that i have heard from any KT-88 Tube

Supposedly these are very good too
https://www.thetubestore.com/northern-electric-kt88

Hi, thank you.

I have MC275 MK6, comes with stock tubes KT88 EH

My ex MC275MK5  remember use SED KT88 =C= 

i replace with this SED to my MKVI and it's better in all freqs.
Bass very deep.

With EH Is agressive and bass very thight-close