• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Dim bulb tester socket 300watt

I think it is important to match the potential power of the device under test with the lamps, otherwise they will not illuminate brightly if you have an issue to investigate.
I used two sockets and two 40 watt bulbs in parallel. One bulb can be removed for a more sensitive tester.
What are you testing?