In some sites with Greek alphabet I read that beta Β stands for B sound, though in modern Greek it is pronounced V.
Didn’t the ancients have any V sounds or what letter did they used for this?
I think they used digamma.
Digamma was not standardized in the Attic alphabet, which became the standard one for the whole Greek speaking world.
The ancient Greeks had no v. They did have a w, but that disappeared from most dialects, and consequently isn’t usually found in printed texts.
That was actually a w.
Although V in SPIonic will give you the digamma. 
Vάναξ
How is it possible? I mean, V-sounds are most common in other Indo-European languages.
You maybe right, but I cannot believe it!
It’s not in Latin (that ‘v’ is a ‘w’); it’s not in Sanskrit (again, ‘w’ is usually transcribed ‘v’); it’s not in some of the early Germanic dialects.
However, the ‘v’ sound develops readily, usually from ‘b’ between vowels or from that ‘w’ sound.
In Koine is the v sound present, or in what time area has it developed?
According to Palmer (The Greek Language, 1980) this started to happen in the first century A.D. This change may not have happened in all Greek speaking communities at the same time.
There is no V sound in Dutch either.
There is a V in the alphabet but it is pronounced the same as the F, or in some cases just barely distinguishable.
I remember that this caused considerable confusion in spelling. “Is this word spelled with a 'Shot f (ie. v) or a long f (ie. f).”
Edit: There are many many different dialects in The Netherlands.
It is very well possible that in some dialects the V is pronounced as a V.
Many dialects in The Netherlands. 
So, how you speak must depend on which side of the street you live on? 
the greeks used either the ou diphthong, or the consonant b, to represent the (latin) “v” sound, which is like our “w” as others have said above. they didn’t have our “v” sound (or the related “f” fricative).
e.g. to write Octavius, they wrote )Oktaoui/a, and to write “Aventine Hill”, they wrote to\ )Abenti=non. see woodhouse:
http://colet.uchicago.edu/cgi-bin/chuck/woodhouse_pages.pl?page_num=1018
http://colet.uchicago.edu/cgi-bin/chuck/woodhouse_pages.pl?page_num=1003
Seems strange doesn’t it, a country as small as that, having many dialects. One province of The Netherlands (Friesland) claims to have its own language, and I think they are right (though I usually tell them that it is not a language but a speech impediment.)
What about the J sound? Did they ever have it?
For a moment I was about to say, “yes, of course,” but I think I should verify which version of that sound you’re asking about.
Like the ‘j’ in job? No.
Like the ‘j’ in ‘ja’ (Gmn. “yes”, English ‘y’)? Yes. But it went away in the historical period for the dialects most of us worry about.
Like the ‘j’ in ‘jour’ (Fr. “day”)? No.
hi john, they didn’t have the english “j”.
(but in a sense they had the latin “j”, i.e. consonantal “i” (where “i” sounds like “y” at the beginning of the english word “yes”), which is where our “j” comes from.
for greek diphthongs ending in “i” followed by a vowel in the next syllable, e.g. )Axaioi/, vox graeca says that the vowel in the next syllable is pronounced with a consonantal “i” (so the last 2 syllables sound like “igh-yoy”). the same thing happens in latin in certain circumstances.)
Don’t they use the letter ‘w’ for v, like in all modern German languages, whereas ‘v’ stands for f?
I know ‘wat’, pronounced vat, for ‘what’, ‘wie’ pronounced ‘vee’, ‘waa’ for ‘vaar’, and a lot of other words.
The only other Germanic language I’ve studied is German but that was 27 years ago. Maybe Emma can enlighten us regarding Modern German.
In Dutch the w is not pronounced like a v. Pronounce the English w with your upper teeth touching your lower lip without a lot of air escaping, then you are pretty close to the Dutch w.
Sorry for the amateurish way of discribing it, I’m a carpenter not a linguist
Interesting… that is how I pronounce a Latin V.
Is v not pronounced always this way?
I mean, how many ways do exist there to pronounce a v-sound?
I speak v by low lip against upper teeth and a lot of air escaping.