To Steel
According to Jesus no one has seen or heard the Father. So the question is who spoke and manifested Himself in the OT. Manifestations were Jesus appearing in the OT, As to who spoke that could have been the HS or Jesus.
Jn 6:46 Not that anyone has seen the Father, except He who is from God; He has seen the Father.
Jn 5:37 And the Father Himself, who sent Me, has testified of Me. You have neither heard His voice at any time, nnor seen His form.
John 1:1 is not referring to Jesus appearing in the OT. Note 1a, In the beginning was the Logos. John is referring to the beginning of time and space. Note who is with the Logos in the beginning, = only God.
I agree it was Jesus appearing in the OT, but disagree John 1:1 is referring to such events.