[bobbyd1200]

I am restoring a Philco 37-60. The am reception is very good, but the shortwave is very weak. Run 6 Philco removes the ground off G3 and adds it to -2.5v.
My radio still has it to ground, question if I put G3 to -2.5 volts will that increase the sensitivity for shortwave.

[morzh]

The suppressor grid (if by G3 you mean the S) is usually at the Cathode potential, which in this case is GND.
I am not sure how it would affect the sensitivity, if moved to negative potential.