Lab-grade test gear for a fraction of the new price. Which used scopes, meters and generators to buy, and what to check first.

Only if the seller can back it up. A sticker or the word in a title proves little, since anyone can print a sticker and it doesn't say what was measured. What counts is a dated certificate from a named lab, with measurement data, for that serial number. Check the serial on the certificate against the one in the photos. For hobby work you rarely need any of that. Two meters that agree on a known reference tell you most of what you need to know.

Check the mains setting and the fuse. A lot of older bench gear has a line-voltage selector, and an instrument shipped from a 230 V country may arrive set for 230 V. A unit set for 115 V and plugged into 230 V can blow its fuse or damage its power supply. Make sure the selector matches your mains and the fuse matches the rating for that setting. On a meter, test the current fuses before you trust a current reading.

For audio and analog repair, yes. A Tektronix 465 is a 100 MHz scope with a live trace, no menus and full service documentation, and a 2465B takes you to 400 MHz. Where analog falls short is catching a single event, like a glitch at power-up, because nothing is stored. If you work with microcontrollers or digital buses, a digital scope such as a TDS 3054B is the better start. Either way, buy one with its probes.

"Powers on" means someone plugged it in and something lit up. It doesn't mean it measures correctly, or that a scope shows a trace. Ask for a photo of the display after the power-on self-test, with any error code visible, and for a scope, a probe on its calibrator output. Treat "untested" as not working until you see otherwise. It sometimes means the seller couldn't test it, and sometimes that they tried.

They're one family. Hewlett-Packard built test and measurement gear from the late 1930s until 1999, when it spun that business off as Agilent Technologies. In 2014 Agilent spun its electronic measurement business off as Keysight. So the same model can carry any of the three names depending on when it was made. As a rough guide, an HP badge means 1999 or earlier, Agilent means 1999 to 2014, and Keysight means 2014 or later.

Start with a good handheld multimeter, since you'll use it on everything and it has to be safe on mains. Then get a scope, because seeing a signal is how you find most faults. A bench power supply with a current limit comes third, then a bench multimeter, which adds resolution and lets two meters check each other. Signal generators and spectrum analyzers come last, and only if you work with radio.