Tektronix 2465B Vertical Adjustment Amplitude Distortion
I've recently got my hands on a Tek 2465B. The only issue I'm having is that increasing the vertical position of any waveform on channel 1 or channel 2 causes the displayed amplitude to drop. As long as the DC level is roughly below the center graticule, there is not amplitude distortion. However, if the waveform higher, the amplitude drops off to roughly half. This problem only occurs on channel 1 and 2, not channel 3 and 4.
Here is a video of the issue: https://youtu.be/RgNdBXvQveA
I've read people having similar issues due to the U400 hybrid. Is this the likely suspect? Would it be a power supply issue? Seems doubtful.