Hi Frank,
The capacitance of a coil assembly is the sum of the parasitic capacitance of the coil itself, the capacitance of the cable and the capacitance between the coil and the grounded screen. This total capacitance is not changed by the influence of an electrostatic charge. The charge built up on a coil case in hot dry conditions, may be transferred to the coil screen and hence to the coil in general and the rest of the electronics via the cable, but as everything ends up at the same potential, nothing untoward happens. Unless, that is, there is a path to ground via the operator, then there can be a steady discharge or in some cases a spark which may cause a loud spike in the audio.
Eric.
