Hello Peter,
The advantage of the AR-47 Nuvistor plug-in: no additional changes inside the mic are necessary to re-convert to VF14 once the plug-in is removed. The mic will be 100% stock again.
The required higher Nuvistor voltage of 110VDC was obtained by replacing one of the four 1KΩ dropping resistors in the original NG power supplies with a wire bridge, and placing that resistor in parallel with an existing one.
Once the wire bridge has been removed and the resistor soldered back in its place again (by a qualified technician, of course!) the NG is also back to stock, ready to power a VF14-equipped U47/48.
When it's done, it will look like this: