Just picked up a 64 Princeton amp, and the tremolo (vibrato) is very weak. Up to 10 intensity it's just on the edge of usable. Is this typical of these amps? If not, what do you think the cause of the problem is? Here's a sound clip illustrating the problem. The first sequence is my 64 Princeton with intensity at 10, speed at 1. The second sequence is my 68 Vibro Champ with the same settings.