There are a MAYBE 4 ways to "pad" a tube microphone depending on the circuit.
One, the standard cap from grid to ground, cap divider network
Two, reduce the charge voltage to the capsule(this might be the best if possable)
Three, remove the cathode bypass cap if the microphone has one This changes the sound because the tube has more feedback.
Four, if it is a charge amp circuit increasing the feedback cap can reduce the gain to a point.
Takes some pictures and/or trace the circuit. We can go from there.
