A problem with my oscilloscope

Hello

I have a problem with my old tube Telequipment 43A oscilloscope, I use a sine wave generator who work perfect and have only .01 % distortion, but wen I feed my oscilloscope with any sine waves it's kind of oscillating alway's at the right side of the sine wave in the screen of the scope. It is doing that only with my scope, so it's not a problem with my sine wave generator

Here a link of a photo of that, I was very close so it's bit out of focus photo and it's hard to catch the sine with my camera.

What can by the problem ?

Thank

Gaetan