In the original trilogy, Darth Vader is "the face and voice of the Emperor" and that Darth Vader is believed to be the very last of the Force wielders, per the words of Governor Tarkin in ANH--as the galaxy is unaware of the Emperor's Sith Religion and darkside force powers.
While privately immersed in his arcane studies and in the Empire's politics, Palpatine has Darth Vader to do his dirty work. This is why we don't see him in the original trilogy using a lightsabre but using the force and force lightning.
And by the way, in ROTJ, as the Emperor and his dignitaries are walking through the hangar to the Thrownroom with JerJerod, Darth Vader, and other Imperial officers, Palpatine is speaking pretty loudly with Vader about how together they can turn Luke to the Darkside of the Force.
This makes me think that with the second Death Star, his belief that the Empire will ultimately win against the Rebellion, and Luke going to the Darkside, Palpatine reveals he is a force wielder of the Sith for the Empire and galaxy to know.