After various experimenting with PC developers I want to share following recipe

Sodium Sulfite 50g
Ascorbic Acid 8g
Phenidone 0.15g
Borax 15g
Sodium Citrate 10g
Potassium Bromide 0.5g
Water 1l

The developer has a strong buffer on the basis of Borax and Sodium Citrate. Produce negatives with fine grain, normal contrast and very good sharpness. Starting dev.time 6-7min at 20C

Kodak Double-X @200 in RD-105 6min