This tube power supply circuit uses a pilot light as a fuse. If there is a problem with the source, the voltage on the lamp increases and it burns out, interrupting the negative supply to the tube. The circuit is from a 1944 documentation.

This tube power supply circuit uses a pilot light as a fuse. If there is a problem with the source, the voltage on the lamp increases and it burns out, interrupting the negative supply to the tube. The circuit is from a 1944 documentation.