'but receivers should not be brazed - not even hard-soldered.'

Hard-soldering IS brazing. Soft-soldering is what you do on copper pipe with various alloys of soft metal like tin and even silver. Can't use lead on plumbing pipe anymore but there's still a load of it out there. Even if this solder contains silver, it is not silver-soldering, which requires about twice the temperature of soft-soldering, with iron and steel getting 'orange-hot'.

https://en.wikipedia.org/wiki/Solder#Solder_alloys