Attached below is my HB transmitter biasing and negative peak limiter circuit. The only mods I have left to do are to find a better 10H higher voltage choke (1000V min) for the screen circuit then modify the fixed control grid bias supply to where it's -200V on idle and then switches down to -100V during transmit for safety biasing. Both the control grid and screen supplies are regulated with VR tubes. The control grid supply mod will be the tricky one. I think I can easily make the control grid supply switch from regulated -200V to -100V if I just tap into my PTT control circuit. The trick will be in configuring everything and making it switch between the voltages without using a mechanical relay if possible. I want it to be all electronic. I may need to use an SCR or two. The control grid supply was designed for two 4-400's so I think a voltage divider setup should work because the supply will still have enough current. Maybe even just tapping it between the two series VR tubes for the lower voltage would work as well if not better. The whole design idea is to have -200V on the control grid during idle like when spotting signals via the receiver and not have the RF exciter's load shift and possibly change frequency like it might if it was always at -100V instead then gets blocked by D4 and D5 when it increases more negative during transmit with RF drive applied which in turn also provides 100% grid leak bias for optimum control grid modulation. P.S. The 4-400 is a PL 4-400CG designed for +500V on the screen and -200V on the control grid.