I should also mention that a very well heeled audiophile, and dear friend, recently sold his 300B monoblocks and moved to a pair of 45 amps that he had long dreamed of owning. The buyer of his amps didn't want to pay a premium for his nearly new (125 hours) Elrog 300B's (second version). So he was left with those after the sale. He kindly gifted them to me for use in my new monoblocks. These are clearly exceptional tubes, but I don't think anyone would describe them as having significant warmth. 

I own Takatsuki 300B they are much warmer and more detailed then the Psvane 300B. Which are the only other ones I have tried. But lots can be gained from AI. Subject to verification of course. 
 

1) Overall tiered ranking by “warmth”

Warmest → Most neutral/lean

1. Western Electric (NOS 40s–60s) – golden, saturated midrange, plush bass bloom, sweet top.

2. Takatsuki TA-300B – rich and organic, a touch drier than vintage WE but still lush.

3. Sophia Electric Royal/Princess – romantic color, smooth treble, forgiving.

4. Psvane ACME / Art Series – weighty and saturated, slightly softer edges.

5. Linlai Elite / E-300B – warm-tilted, good tone density; a bit fresher than Psvane.

6. Elrog ER300B-Mo (moly plate) – warm with grip; adds meat without murk.

7. KR Audio KR300B – neutral-warm, muscular, less glow than above.

8. Western Electric (current production 2021+) – tasteful warmth, more linear than vintage.

9. Emission Labs EML 300B (solid plate) – mildly warm-neutral, taut low end.

10. Elrog ER300B (std) – very balanced, barely warm.

11. JJ 300B – generally neutral; can read a bit dry/flat depending on amp.

2) Overall tiered ranking by “detail”

Most resolving → Softest

1. Elrog ER300B (std) – speed, inner detail, transient snap.

2. EML 300B (solid) / EML 300B-XLS – clean edges, big dynamic envelope.

3. Takatsuki TA-300B – high resolution with natural textures.

4. Elrog ER300B-Mo – resolves almost like ER standard but with more tone weight.

5. KR Audio KR300B – incisive, dynamic, good micro/macro contrast.

6. Western Electric (current production 2021+) – refined detail, non-fatiguing.

7. Linlai Elite / E-300B – good detail for the price; slightly rounded leading edge.

8. Psvane ACME / Art Series – pleasant resolution but prioritizes density over edge acuity.

9. Sophia Electric Royal/Princess – soft focus, seductive.

10. Western Electric (NOS 40s–60s) – not “hi-fi etched”; detail is there but wrapped in golden warmth.

11. JJ 300B – serviceable; less micro-info and ambient air.

3) Placement map (quick chooser)

• Warm & Smooth (romantic, forgiving)

  • WE NOS • Takatsuki • Sophia Royal/Princess • Psvane ACME/Art • Linlai Elite

• Warm & Detailed (weight + resolution)

  • Elrog ER300B-Mo • Takatsuki • KR 300B (on the line) • WE 2021+

• Neutral & Detailed (speed, clarity, stage precision)

  • Elrog ER300B (std) • EML 300B / 300B-XLS • KR 300B • WE 2021+

• Neutral & Easygoing (budget-friendly, honest)

  • JJ 300B • Some Linlai/Psvane non-flagship lines

4) Best picks by goal & budget

• “Maximum warmth & tone color” (cost-no-object): WE NOS → Takatsuki

• “Warm and high resolution”: Elrog ER300B-Mo → Takatsuki → WE 2021+

• “Neutral, fast, and resolving”: Elrog ER300B (std) → EML 300B/300B-XLS → KR 300B

• “High value, warm-leaning”: Linlai Elite / E-300B → Psvane ACME (watch QC)

• “High value, neutral-leaning”: JJ 300B (reliable, less magic)

5) Matching notes (to land your target sound)

• Already warm amp/speakers (e.g., lush SET iron, Sonus faber-type voicing): Prefer Elrog ER300B (std) or EML to avoid syrup.

• Lean/quick systems (e.g., high-resolution horns, very revealing DACs): Takatsuki, WE 2021+, Elrog-Mo, or Psvane ACME to add body.

• If bass is loose: EML or KR for grip; Elrog (std) tightens too.

• If treble is hot: Sophia, Psvane ACME, or WE 2021+ for sweetness.

6) Caveats that matter

• Sample/amp variance: 300Bs react strongly to operating points (plate voltage/current) and output transformers. A “neutral” tube can sound warm if biased differently.

• Reliability/QC: Boutique lines can vary. Favor trusted dealers, matched pairs, and solid warranty support.

• Break-in: Expect 50–150 hours for bass and treble to settle on most premium 300Bs.

• XLS/High-current variants (EML, KR): Check your amp’s allowable dissipation—these can run hotter and change voicing (often tighter, more dynamic).

I did the query by warmth and detail... to be able to separate warm but mushy tubes. Typically you want both. 

ghdprentice thanks VERY much form your information. Of course, the 300B tubes noted as warmest are the two far beyond my budget, the Western Electric and the Takatsuki. And, even if I had the money, I wouldn’t touch a pair of Western Electrics given the apparent drop off in quality and sound over the past year with recent production. Next up would be the Sophia Princess, and, given the experiences with short life and failure that friends of mine and I, as well as forum members, etc. have had I wouldn't take a pair of those for free. Doesn't look promising. 

Regardless, the input is greatly appreciated. 

https://forum.audiogon.com/discussions/coincident-frankenstein-mk-2-amps

Hi nightfall, I responded to your other thread regarding your Coincident amps. The above thread which is 12 years old is still relevant today for owners of Coincident Frankenstein amps imo. There is a good discussion regarding which 300 B’s work well with the Franks. Also, some good info on rectifier tubes. Charles1dad and others give valuable insight in this thread. 

As for seeking more warmth, I too felt the same way when I first got my Franks. I had commented to Charles way back when I first got my amps that I wanted more “meat on the bones.” Instead of replacing the stock 300B tubes with a notably warmer 300B, I went with the EML 300B XLS tubes, just like Charles and others in that thread did. The EML is a neutral, very natural sounding tube that allows you to hear differences in cables and source components. It is not hyper detailed as the above AI response might suggest. When I wanted more scale and weight (some might call this warmth), I accomplished my goal with cables, careful vetting of dacs, and improvements to my analog playback system. One of the main attributes of the Frankensteins are their transparency and a warmer tube might compromise this imo. For me, it has been a blast over the years to more easily hear the differences between cables, dacs, cartridges, etc. If it were me, I would stick with the Elrogs, which Charles also loved, and build around them, assuming your Elrogs are newer production and over the QC issues of the past.