I just remembered another one!
Vintage Marshall Plexi half stack
Not sure the exact year or model, but it was 100w. It was the first time I ever used a Plexi. It belonged to a guitarist from another band and we had to share gear for this show. I had no idea how to dial it in and it was a small room and I needed clean, so we had to keep the volume level low (no master volume on the amp).
It was a night of the worst hard, harsh, clanging, ice-pick in the ear tone I’ve ever had to deal with!
I thought I hated Marshalls for a long time after that night. Turned out I just needed to learn how to use them