"Whether to pronounce Yahweh’s Name with a “v” or “w” hinges on which letter accurately transliterates the sound of the Hebrew letter W or “waw” in the Tetragrammaton, YHWH.
"We must take into consideration the ancient pronunciation of the waw and whether “v”, “w” or “u” as we know them accurately reflect that ancient pronunciation. The following information is derived from a number of sources, including G.B. Palatino’s Lettere Romane (1545). ‘U’ and ‘W’ are variants of ‘V’ which was being used for two different sounds in medieval England. ‘U’ was introduced to give a soft vowel sound as opposed to the harder consonant sound of ‘V’. ‘W’ began as a ligature. Two ‘V’ letterforms were joined into ‘VV’ to represent ‘double U’ in 12th-century England. Those who use the “v” form of Yahweh’s Name (Yahveh) should note that the Name is spelled “Yahweh” in almost all academic publications, many by people well-studied in the Hebrew language, including Hebrew speakers. Hebrew linguists believe the third letter waw was in ancient times pronounced as “w” (hence it is named “waw”).
"In later Hebrew its pronunciation, influenced by European languages, was changed to “v” and the letter was later called “vav,” according to the Encyclopædia Judaica. The Judaica shows that the semitic languages nearest Israel use the “w” pronunciation as opposed to the “v” pronunciation found in those speakers of Hebrew living in or closer to Europe. Those using the “w” sound include Jews of Babylonia, Yemeni, Morocco, Samaria, the Sephardi (Temple Hebrew) and Portuguese. Those using the “v” sound of “waw” include Hebrew-speaking communities in Italy, Poland, Germany, and Lithuania. These Europeans picked up the Germanic “v” and transferred it to the waw.
"The change from W to V is very well known, for example, in most of the continental languages like German (also the descendants of Latin). We know from historical comparisons that direction of change in Latin was from W to V. English has remained faithful to an old W sound for over six thousand years, while it changed to V in Late Latin almost two thousand years ago (but had not yet changed in Classical Latin). The “w” is formed by putting two “v” letters together, but it is called a double-u because it is made up of two letters originally pronounced as we do the “u.” One needs only to look at old government building architecture with inscriptions bearing a “v” but pronounced like a “u” to see that the “v” was originally a vowel sound like “u” (e.g. bvilding, Jvly).
"It was not until the dictionary was published that a decided difference was made between the “v” and the “u.” It is more than coincidence that the U, V, and W occur together in our alphabet; it shows a common relationship that these letters had in derivation and similar pronunciation.
"The v is a consonant that some have used for the sound of the Hebrew waw in Yahweh’s Name (Yahveh). The problem is, the waw in His Name was considered a vowel anciently. In fact, all the letters of the Tetragrammaton are called vowels by Josephus (Wars of the Jews, 5.5.556) as well as by Hebrew grammars. Bagster’s Helps to Bible Study also says these are vowel-letters in the sacred Name, “as having been originally used to represent vowels, and they still frequently serve as vowels in combination with the points.” Bagsters says the waw represents the letters o or u.
"Another authority says, “The sound of waw a long time ago wasn’t ‘vav’ at all but ‘w’ and ‘w’ is weak. The Yemenite Jews of Arabia who retain an ancient, correct, and pure pronunciation of Hebrew still pronounce the waw as ‘w,’ as does Arabic, the close sister language of Hebrew,” How the Hebrew Language Grew, Edward Horowitz, pp. 29-30. As the online Wikipedia notes: “There was no ‘U’; instead, there was the semi-vowel ‘V’. There was no ‘W’, although ‘V’ was pronounced as the modern English ‘W’.” As for the “j” in “Jehovah,” the letter J is the last letter to be added to our alphabet. ‘J’ was an ‘outgrowth’ of ‘I’ and was used to give a sound of greater consonant force, particularly as the first letter of some words. It was used interchangeably with the letter “I” at first, showing that its original pronunciation stemmed from the vowel sound of “I” and only later got its “juh” sound through French influence." (