Vibrato problem, please help!

hello,
thanks for looking. i just picked up a music man 212 i believe. it's in a re-tolexed box (orange, so it looks quite unique). it's got new speakers and all the wiring looks sound. anyway, the vibrato doesnt' work. however, when i turn up the amp the hiss that results has vibrato. my guitar comes through clean, but the"noise" created by the amp is definetly coming in and out depending on the "speed" setting of knob. is this an easy fix? any ideas on what could be wrong? help is greatly appreciated
thanks!
petereneeheartfelt@Hotmail.com

Pete You may need to adjust the trim pot, the one that is to the left of the Bias pot. Or you have a bad 2N4091 Or 2N3391.