have old radiator, cannot adjust level of heat using attached regulator, tried to tighten it etc, but heat is at full blast.

if the valves are as old as the radiator them the chances are youll need to change them over to new ones as the rubber washers inside them have gone hard and brittle with the heat, hopes this helps

Is it a trv? If it is not it will not regulate the heat. If it is a trv then it is either stuck an need replacing or has been installed on the return rather than the flow.... Check to see which pipe gets hot first on the rad, this will be the flow

If your going to change the valves, always change both sides