The GA-8T (or the GA-8T Discoverer) was based on the regular GA-8 but with the addition of Tremolo. Like other Gibson amps, the GA-8T changed in its covering material during its run. Initial, it had a gold wrap which was replaced by Tan in 1963 and then Black in 1965. 

Years of Production: 1960 - 1967

Features: 1 x 10-inch speaker, 2 inputs,  9 watts