I walked a Tektronix boat anchor out to the dumpster at one place I worked because I didn't have a place to put it. Don't know the model number but I regret it to this day. I actually had it in the trunk of my car but changed my mind at the last minute. It's been almost 15 years and I'm still mad about it. I also tossed a broken Keithley bench DMM and a broken Micronta DMM, both of which had sentimental value, during a rather severe fit of cleaning. I got tired of shifting them from one "I'll get to it" pile to another.
Ditto an elderly Dumont oscilloscope that wouldn't power up, and a Sencore tube oscilloscope (PS148, I think) that would trip a breaker. Both of those had sentimental value too-- given to me by a family member that had since passed-- but sentimentality gave way to practicality when I realized I could hardly walk around the piles of junk any more. They were pretty far gone, and while I know they could've been rescued I also knew that I wasn't the person to do it. A nearby HAM operator wound up with them, I think.
I've sold lots of old vacuum tubes and a few tube radios that were full of mouse nests, just to get them out of the way. Truth be told, I regret selling the cool old red-and-black RCA vacuum tube caddy more than its contents. I'd like to find another one to use as a vintage-looking toolbox for mobile repairs, but the shipping costs usually kill that idea, and the only one I've found at a local yard sale was too warped and rotted to rescue.
I tossed a BUNCH of NOS TV parts when it was clear that I couldn't even give them away. NOBODY wanted that stuff.
I gave a Tek 922R to a friend when I upgraded. I don't regret it (well, I mostly don't regret it), but I told him that I wanted first right-of-refusal if he ever decides to send it on its way. I grew fond of that scope despite its 15 MHz and huge footprint.
I DID manage to keep an old Heathkit SO-4552 oscilloscope that has been in the family since the late 1980s, despite the fact that it spent years in a damp basement and wouldn't display a trace when plugged in. Turned out to be an intermittent connection on a wiring harness connector. I spend some time cleaning going over connections and contacts with DeOxit, after which it worked about as well as you can expect from a Heathkit scope made by Pintek. It has a component test function which is occasionally useful, but I'm not going to kid you-- this one is around for sentimental reasons. And it's STAYING.