40年代的威廉逊已用上 440VAC Motor-start capacitors 起动电容 - 纸质油浸 oil-filled paper types.
Important Note:
Although not shown in the parts list the actual filter capacitors used were oil-filled paper types.
These offer a superior tonal quality and overall performance than simple electrolytic types and should be used where practicable. 440VAC Motor-start capacitors may also be used if preferred.
These non-polarised capacitors will have contributed significantly to the popularity of the "Williamson sound".