ecossais

“As I know, in modern English the vowel [ʌ] is no more pronounced as...”

ouch!

The vowel [ʌ] must always be pronounced the same, since it's an IPA symbol that describe a sound. IPA symbols don't change, they are defined that way, and they remain so, so that we can describe some sounds.

What happens is that dictionaries use a set of symbols even if they don't represent the real pronunciation, so you have a kind of "phonemic transcription", and not real "phonetic transcriptions". For example, from a dictionary you can understand that "bug" and "sub" have the same vowel, or that "teacher" and "better" rhyme, but it doesn't tell you how to pronounce them exactly.

If dictionaries had real phonetic transcriptions, "but" would be more like /bɐt/ (in some American dialects), but then it would be highly dependent on the dialect chosen as the standard.

So yes, it's confusing. Dictionaries are not exact or perfect. The set of sounds and features you use in your speech depends on your accent, and dictionaries don't take that into account. As an example, every dictionary includes /t/ in transcriptions of words like "twenty", but many Americans skip those kinds of /t/ after /n/, and so they just say "twenny"... yet no American dictionary skips it in the transcription.

I don't know if I understand your problem, but you are right, transcriptions in dictionaries are not accurate. But I don't know what to say, because it varies from dictionary to dictionary...I'll just give you a few examples taken from Longman Dictionary of Contemporary English:

Thought: /θɔːt/ - both US and UK.

If they had chosen a better transcription they would have written /θɑt/ for US English. That's how some Americans say it, but some are not cot-caught merged, so some might say something like /θɒt/ or /θɔt/. In the UK, maybe it's often more like /θot/, but I don't feel too sure about all these sounds, LOL.

So, as you can see, Longman's choice to just write /θɔːt/ can't be accurate, and it's up to the reader to understand how it would come out in their own accent. It can be confusing.

Damn: /dæm/ - both US and UK.

This seems ok, but the truth is that many (maybe most) Americans actually say something like /dɛəm/ or /deəm/, like a kind of diphthong. So, this is another case where the true phonetic transcription would be different.

So what you have is that dictionaries have phonemic transcriptions which use IPA symbols but are not phonetic transcriptions... which is odd. Some dictionaries at least use their own set of symbols, which makes their phonemic transcriptions less confusing.

Dictionaries that use IPA should use them correctly and switch to phonetic transcriptions, in my opinion. It would be nice to have a dictionary where you can find pretty accurate phonetic transcriptions in the most common accents/dialects. Something like: Ten (US /tɛn/ - US Regional & AAVE /tɪn/ - Etc.) or Bee (US /biː/ - London /bɪi/ /bei/ - Etc.)... That would be so cool! I suspect doing that would be so difficult that to have accurate transcriptions that make sense... basic IPA wouldn't be enough.