Hi folks. I brought home someone's homebrew amp project. It uses a pair of 813's, cathode driven, with grids/screen (pins 3, 4, and 5) tied directly to chassis ground. It did not come with a power supply but I have a 1400 vdc supply with -130 vdc for bias. I realize this isn't quite as much plate voltage as the 813's want but it should work. How would you suggest I bias 813 tubes with the grids at DC ground? All designs I have found for this tube bias and feed the grid, not the cathode. Can I apply bias to the cathode? My supply has the center tap of the HV transformer going through a choke and getting rectified to 500 vdc, that could be regulated for screens but I'd prefer the simpler construction of grounded grid, and I'd rather just ground that center tap.