The following is an excerpt from Dr. Thomas Holland's Crowned With Glory, ©2000, used with permission.
Acts 19:2 - "Have ye received the Holy Ghost since ye believed?"
"He said unto them, Have ye received the Holy Ghost since ye believed? And they said unto him, We have not so much as heard whether there be any Holy Ghost."
Some have claimed the KJV is in error in its use of the word since and suggest the passage should be rendered "Did you received the Holy Spirit when you believed." The Greek phrase Ei pneuma agion elabete pisteusantes is literally translated as, "[The] Spirit/Ghost Holy did ye receive having believed?"
This phrase stands in the Greek aorist and refers to past time; thus, we have the past tense with the words received and believed. This would establish the translation when you believed as correct as it relates to the Greek itself. However, the English word since also reflects past tense and is correct as it relates to the Greek text. H. E. Dana and Julius R. Mantey, noted Greek grammarians, address the use of the aorist. They write, "The fundamental significance of the aorist is to denote action simply as occurring, without reference to its progress."  Therefore, the words since or when both reflect the proper use of the aorist. In reference to what is called the Culminative Aorist, Dana and Mantey add:
The aorist is employed in this meaning when it is wished to view an event in its entirety, but to regard it from the viewpoint of its existing results. Here we usually find verbs which signify effort or process, the aorist denoting the attainment of the end of such effort or process. 
In this regard, the word since is proper as it relates to the aorist tense. It can indicate a past action, but one that was attained through a process. Dr. George Ladd recognized this and stated of this passage, "The Greek participle is having believed, and it is capable of being translated either since ye believed (Authorized Version) or when you believed (Revised Standard Version)."  Therefore, both translations are correct and neither are in error.
 H. E. Dana and Julius R. Mantey, A Manual Grammar of the Greek New Testament (Toronto: Macmillan, 1927), 193.
 Ibid., 196-197.
 George Ladd, The Wycliffe Bible Commentary (Nashville: The Southwest Company, 1962), 1160.