Maybe what you mean is for testing antique radios, test equipment, etc?
A
Variac or variable
autotransformer would fulfill the lower voltage testing function (for example, its good to use a lower voltage or an incandescent light bulb in series when turning on antique equipment for the first time in years)
but it wont supply isolation. Which you also need with old equipment because some of it is not built to modern safety standards at all. Sometimes it has line level voltages in places you could easily make contact with.
Dont touch anything with your body. That old radio chassis or its knob shafts could be hot. And also combine the variac with a medical grade isolation transformer.
How they are connected together is important and other people here know how this needs to be done. (I never work with high voltage, period.)
It may be in the site's sticky documents.
Don't float your scope or other test equipment. That kills people. Get the above setup (isolation transformer, plus variac, or in some cases instead of the variac you can use a power plug modified so that the device under test when power is first applied receives it in series with a 100 watt light bulb) and use it properly.
Also install a
ground fault circuit interrupter socket (GFCI) at your bench so that any shorts in your equipment result in GFCI turning the power off immediately, rather than the short starting a fire or killing you. Between all these things, you should be much safer than you would be without them.
It really gets cumbersome and dangerous to check circuits powered by line voltage. Is there some way to use an AC wall wart (or something else) to do the same test allowing for changes in the values? If so, one could then switch to high voltage if there was good reason to think the component was functional. This would seem an excellent way of testing when one has a known-good board to test against a malfunctioning board. Thank you
It would be even more cumbersome being dead!
Do some research into the right ways to handle the dangers presented by old possibly dangerous line powered equipment.