Vector T-789-C Tube Socket Test Adapter Set, Current & Voltage During the vacuum tube heyday, these adapters would be plugged into a tube socket and then the tube into the adapter. This provided test points above the chassis for making measurements without removing the chassis from the cabinet. These current probe adapters are less common than the voltage-only type. You can still measure voltages at the test points or use the special probe to break into the circuit and measure current. This set is unused in the original plastic box with documentation. It includes 3 adapters: Octal, 9-pin, and 7-pin, as well as a current probe.