I remember using a TU-5 Pulser for this purpose,which used a tunnel diode.
In use,you connected it to the 100 volt calibrator on a 545B or similar,& the TU-5 produced a very much lower level,(but very much faster rise time) pulse which was excellent for checking the 'scope,& for TDR purposes.
I had one hanging around for years,but I don't have a 545B,or anything similar,so no high voltage calibrator.
I thought of making a vacuum tube multivibrator to produce a 100volt square wave,but "put it in the too hard basket".
Eventually,I gave it to a friend who collected 545s.