The SB220 has a separate filament transfomer but since the line feeding it and the plate transformer is the same, any sag on the line voltage due to plate primary current drawn by the plate transformer will affect the filament voltage.
On Monday, December 9, 2024, 10:04 AM, Bill K3HZP via groups.io <hzp_electronics@...> wrote:
I have mixed emotions about NTC resistors.? I tried one on my SB-220 and found that the resistance would change between idle and full plate current.? The large current change caused the filament voltage to change since it uses the same transformer.? Because of the filament voltage change under load, I took it out.?
Bill K3HZP
