2213/Repairs
The 2213 oscilloscope and the 2215 oscilloscopes with the serial numbers B010100-B029389 for the 2213 model and serial numbers B010100-B031639 for the 2215 model both had one dire fault in their PSU design, they had a transformer that supplied too much voltage for the heater filament of the CRT that could lead to premature CRT failure. Tek realizing the problem sent out a letter with instructions on how to fix this issue. The document for this mod is under the service section of the manuals.
If a CRT seems malfunctioning and does not have such modification installed, a burnt-out filament could be the issue on these scopes, requiring CRT replacement to repair it.
It is very important to install this modification if it hasn't been installed in your 2213 or 2215 already.