I just received a ~69/70 silverface Deluxe Reverb that I bought from another forum member. It's in amazing cosmetic shape and sounds great with the exception of the Vibrato. The Vib works but I don't hear any effect until the Intensity is at about 4.5. At 10, it doesn't have the depth I expected. I don't have much experience with Fender amps but I don't think this is how it should be. What components affect the Vibrato depth? Also, from the quick dating I did from speaker codes and tranny stamps, the parts were made in late '69. It has "AB763" on the tube chart but I realize that's probably incorrect. How can I tell for sure?