amp problems

[paolo]

hi
I have an old suitcase 73 which worked perfectly till few months ago. Now the amp starts to play in a strange way: I have less and less trebles, the regulation for bass and trebles doesn't work, when I change tremolo depth volume changes, one of the two big fender cones makes a vibration noise. does anybody has an idea of what's happening to my piano. Is it just an amp problem or comes from the piano?
thanks in advance
paolo

[milwire]

Sounds like a cold solder joint somewhere in the preamplifier circuit, which is located in the keyboard portion of the suitcase. A bad connection such as this will cause unpredictable results as you have described since bias voltages will be off throughout the circuit. Look at the schematic for the preamplifier circuit and the corresponding circuit board layout that are available on the Super Site. Check the bias voltages on IC A1 as a start. Since your tone controls are non functional, I wouldn't be suprised if one of the 15 volt power rails has lost connection to this IC.