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12-31-2023, 03:43 PM
Hi Guys
There is no interaction between the plate winding of the PT and the circuit in the manner described. The cap across the winding is too-low a value to have any such interplay; rather, it is there to help suppress noise, as described in TUT3 and elsewhere in the TUT-series.
The noise suppression function is bilateral in that noise coming through the PT to this winding MAY be suppressed slightly by this cap, while at the same time rectification noise can also be very slightly suppressed. Limiting factiors to effectiveness are the lack of known resistances or impedances for the cap to work against.
In any case, the cap you pulled out is a multi-layer ceramic cap (MLCC) which has quite a range of characteristics good and bad. I would not bother installing anything similar, and broadly would not use a ceramic in that position. "PP or go home".
Considering that the filter caps in the plate supply are rated for 550Vdc, the AC from the winding could be as high as 385Vac, and may be higher with no load. A safety cap rated at 440Vac will work here. Choose a polypropylene types, which in such applications is a box-style format. Yes, there are ceramic safety caps but why go there? As mentioned, you do not really need this cap - the resistors across the first filter cap are far more important for safety.
There is a Technical Article on my site that discusses stand-by switches. Such switches are illegal in some countries.
There is no interaction between the plate winding of the PT and the circuit in the manner described. The cap across the winding is too-low a value to have any such interplay; rather, it is there to help suppress noise, as described in TUT3 and elsewhere in the TUT-series.
The noise suppression function is bilateral in that noise coming through the PT to this winding MAY be suppressed slightly by this cap, while at the same time rectification noise can also be very slightly suppressed. Limiting factiors to effectiveness are the lack of known resistances or impedances for the cap to work against.
In any case, the cap you pulled out is a multi-layer ceramic cap (MLCC) which has quite a range of characteristics good and bad. I would not bother installing anything similar, and broadly would not use a ceramic in that position. "PP or go home".
Considering that the filter caps in the plate supply are rated for 550Vdc, the AC from the winding could be as high as 385Vac, and may be higher with no load. A safety cap rated at 440Vac will work here. Choose a polypropylene types, which in such applications is a box-style format. Yes, there are ceramic safety caps but why go there? As mentioned, you do not really need this cap - the resistors across the first filter cap are far more important for safety.
There is a Technical Article on my site that discusses stand-by switches. Such switches are illegal in some countries.
