The reverb on my old ampeg reverberocket 2 gs12r (1966 i believe) was dying out so I bought a replacement tank (I bought the proper tnak for capacitance driven reverb circuits like this amp has) and now the reverb is back to all its glory! but it has wayyyy too much reverb! at about 1/4 of the way up on the dial it actually starts feeding back with a high pitched whine that wont go away unless I turn the reverb knob all the way down for a minute or two. if I have the knob just below the position that it will feedback it actually sounds really great and lush. The tank is the MOD 9FB2A1C. I didnt have a circuit problem with the reverb before the previous tank died- so could this be the tank itself? I did think the reverb (previous to the last tank failing) was way too bright sounding and I did some mods to counteract that. But just some adding more capacitance in places to lower Low pass filters cut offs and some snubber cap type stuff. Any ideas? Thanks!