Justin get a heater circuit like LAMPI does now it’s not complex really and it makes the heater for 5 tubes perfect as in .2 volts correct and never above. It even has a delay voltage at turn on to keep all tubes even lower for a 5 seconds. This allows the filaments to get hot and no cold shot at startup. By the way most all tube circuits have such a delay
The rework will sort that out. It will also high handle high heater valves like Tesla RD27AS at 9.2 Watts properly.