Ampico A/B Expression
By Craig Brougher
|Patrick Mullarky asked about regulating the Ampico A/B, having only one crescendo and two sets of expressions.
It is actually impossible to give Pat a knowledgeable answer as to the problem of uneven pressures between bass and treble. But one thing you can say for sure-- That cannot happen unless there is something wrong between the two halves of the stack.
The crescendo is simply an air spring. It acts as a variable weight which biases both sides exactly the same. The convenient thing about it is, it can act as a weight for both bass and treble at the same time, and will be exactly the same for both.
Some things which may cause your problem:
1. A Spring pneumatic which is either dragging the regulator wire
or set too open or closed when the expression board is level.
2. A leaking or weak expression pneumatic square. At the first
intensity, they are all clamping.
3. A cocked expression valve, or valve that doesn't want to sit
straight. It may be sitting on its pouch, or its pouch may have
a bit of a leak, partly inflating it.
4. A leaky valve in the stack-- one side or the other.
5. A leaky stack itself-- many times the top veneer is cracked or
the joint is loose, or a supply nipple is loose.
In other words, anything, other than the crescendo, will cause your problem and it's nice to know, since you might have been able to cover it up with two separate crescendos, but not with just one. Your chickens have come home to roost.
(Message sent Thu 1 Aug 1996, 14:40:56 GMT, from time zone GMT.)