The past and present tenses of "read" are spelt the same but have different pronunciation. This question is related to the post Why are the past and present tenses of "read" spelt the same?.
The second basic form of "to read" keeps the a to differentiate it from "red", the colour.
Your use of the term conjugation is very unclear. A conjugation is a table of all the forms a verb can take. All finite forms in active and passive and all infinite forms.