Hi,
As a native speaker of Portuguese I am used to producing these sounds as dental, but after a little study on phonetics I realized they are alveolar in most languages. So I assumed they would be alveolar in Russian as well.
But I have been listening to the Pimsleur lessons and I noticed that I can only reproduce the exact sounds of ть and дь in the dental position (OK, maybe not the exact sounds). I am not able to tell the position of the other sounds because dental and alveolar consonant are not that different, but I am really curious about that because I want to do my best to have a proper pronunciation.
So maybe they are actually dental, and not alveolar as I have thought? Or some of them are dental and some alveolar? Or they are all alveolar anyway?