The power indicator light of the B&K 747B is a 2V 60mA bulb, which can be replaced by an LED. The "short circuit" indicator light is a 50V-60V low-voltage neon bulb, which can be replaced by a 5AG-A-ND.
https://www.antiqueradios.com/forums/viewtopic.php?f=8&t=370143&start=20
https://www.antiqueradios.com/forums/viewtopic.php?f=8&t=370143&start=20