I just picked up an HP 8642A. The fan wasn't working so I replaced it. I see clipping on the top of the output at lower frequencies and it increases with amplitude. By 5000Hz it's good. Perhaps a thermal issue happened before the fan was replaced. Any thoughts on this issue are appreciated. I work on vintage receivers so picked this up for tuner alignment (overkill!) and the inside is a bit daunting. Output picture on my scope is attached.
-Thanks