First, loving the conversations here - delving into the correlated technical stuff. Everyone should have a Tektronix RTA for this hobby, lol. But the last time I used one they were over $50k. That's more than a good pair of interconnects🙄.
It's also intriguing reading that these amps will run Monolith output iron. Kind of curious which series they are based on, but maybe that's asking too much.
Tubes
Over the years I've used quite a few different tubes from NOS to current production - Shuguang, Psvane, JJ, Sophia, Linlai, KR (Kron), EML, Takatsuki, WE. Some brands aren't worth mentioning. In the past I preferred KR in amplifiers as they are wideband, dynamic, and have solid bass. But depending on the system, can come across as a little unrefined/aggressive. I liked them in what I had. (PX4, PX25, 242, and 5u4g)
But with 300b in what I've owned:
Art Audio - They make heat and conduct electricity. About the nicest thing I can say about them
Shuguang 98b - Meh. Pretty darn average across the board. Puts me to sleep.
Shuguang BT - Pretty good in a VAC Renaissance P/P amp. But other places are bright, lacking midbass weight, and little bass
Linlai 300b E - A good step up, decent bloom and detail, a little light in the midbass and down low
EML 300b XLS - Pretty good. Not as nuanced as the best. Depth and width OK, but not the best. Good low end drive. Much better than everything listed above.
Takatsuki - Excellent tube. Best bass drive. Good Detail. Depth and inner resolution good, but not the best.
WE 300b new production (2022) - Excellent detail, inner resolution, nuance. Holographic. Quiet. Appropriate bass weight and definition. Not as punchy as the Tak or the EML. That will depend on your system. 5 year warranty and projected long life. Love this tube in my SET amp. Well worth the money.
So I find a huge performance delta in the list. Spending the money will be rewarded, probably more in SET than P/P, but that's speculative.
Oh, regarding comments about DAC's made earlier, I concur with Don who has a Lampi Pacific 2 with DHT output, my Lampi Horizon dac is the most significant piece in my system. But there are no unimportant pieces.
Very curious to hear user comments once the production Blackbird and Raven hit the wild.