I did: something like 180 V RMS into a high-resistance load which dropped to about 30 V with even a nominal load - I managed to find a 25 W cooker bulb and lashed up a connection to it and even that caused the voltage to drop immediately. I *think* (though it was a while ago and I may have forgotten) the voltage returned to 180 when the load was removed (leaving just the voltmeter) so it wasn't just that the battery was flattened. That's why I wonder whether the inverter was shagged-out.
But I should have persisted with it... Ah well.
They had all manner of surplus electronic kit from various places: TVs, tape recorders, radios, record players. I even saw a broadcast-standard open-reel video recorder of some strange format. Great big appliances with big knobs and valves or else circuit boards of discrete transistors - not an IC in sight! I think the manual for my scope was dated 1968 so the technology dated from then. I bet nowadays you can get a little oscilloscope adaptor with USB output for recording and display on a PC. The shop was a real Aladdin's cave of stuff - shelves full of things that most people probably wouldn't even have been able to identify. It was a shop within a terrace of houses - a real back-street "you'd never know it was there" place. That was in the mid-80s; I doubt whether it's still there now.