Another option is to increase the CRT filament voltage. The easy way is to set the mains voltage selector to LOW.
Since the CRT filament is powered directly from the main power supply transformer, this increases the filament voltage enough to often cause a significant increase in intensity.
This will also increase the the voltage regulator dissipation, but with the large heatsink of the rear casting, this is not really an issue.
Be aware that the CRT filament is raised 3KV above ground.
There are few options for an excessively weak or dead CRT in the 576.
Years ago I had considered attempting to install a CRT from the 1420 or 528, one without an internal graticule. These are at least somewhat similar in physical size, although smaller, and use a similar low HV.
Good Luck with your effort.
