I've spent about 2 years chasing down the various Vintage 30 theories, including getting some very interesting inside information. I've owned 12 Mesa cabs and 100s of individual V30s of all types and have tested them in quite a scientific manner.
The long and short of it is that the batch the speaker comes from is far more important than anything else. Variations/changes in cone manufacturing are the reason why there is such drastic variety in sound from V30s, which results in a lot of the paradoxical comments you read.
From the early '90s up to about '99 V30s (all types - T3903/3904s and T4335/T4416s) are a lot airier/brighter than anything that has come afterwards, but with less upper midrange so they aren't harsher, just brighter. Around 2000 they darken quite a bit and get more of an upper mid presence. In 2001 they get extremely dark, to the point that you have to mic them almost dead centre to get a bright enough sound from them, but by 2002 they've recovered and sound closer to the 2000 models but with more "shrieking" high frequency spikes that have remained to the current day. The 2003 is a golden year as far as I'm concerned - they're really smooth and warm sounding with just enough bite. 2004 and 2005 sound close to 2002s, then from about '06 onwards the start to develop a more "shouty" midrange (more in that 1-2.5k area) that remains to this day. From about 2011 onwards V30s sound pretty consistent and similar to those you would buy new now, and here I'm referring to both Chinese and UK made V30s.
Mesa changed from rating V30s at 70w to 60w sometime around 2010, but the speakers are the same.
These are some substantial take-aways I've found after lots of testing:
- If you compare a Chinese and UK made V30 of the same ohmage from the same year with the same cone batch code, that have seen similar use, they sound incredibly similar. The difference only comes down to the glues used, which does make a difference but doesn't cause a massive shift in voicing at all. Of course most people compare Chinese and UK made versions from different batches and they sound notably different because of variations in the cone.
-You HAVE to compare speakers of the same ohmage. 16ohm speakers always sound brighter with less midrange, where 8ohms are darker and more midrangey. It's the impedance of the each speaker that matters here, not the ohmage of the cab. I.E. when comparing a 4x12 with 4x8ohm speakers wired at 8ohms total, and a 2x12 with 2x16ohm speakers wired at 8ohms you have to take into account that the speakers are brighter in the 2x12 even though overall both cabs have the same impedance.
-If there is a difference between UK-made "Mesa" V30s (T4335/T4416) and UK-made regular V30s (T3903/3904), I'm yet to find anything notable. I've tested this a lot and when comparing between each type with the same cone batch codes they sound as similar as any two of each type (there is always a large variation in sound from one speaker to another, even if they are sequential off the production line). The odd thing is that Celestion decided to give them separate T-numbers. I've heard this is because of the fact the sticker is rotated 45 degrees on Mesa spec V30s, but pre-2000 the stickers were in fact oriented in the same way as regular V30s, so this doesn't make sense.
