In article , Paul Burridge
writes:

They look worryingly inductive on visual inspection (there are metal
foils rolled up in thar by the look of it.) And yet the CPC catalogue
says that their properties make them ideal for use in filters. Has
anyone any remarks (favourable or otherwise) to make about the use of
this type of cap in filter apps?

BIG difference between two types of rolled-foil style or "tubular"
capacitors even at MF. For MF or even LF, use the low-inductance
"extended foil" type; manufacturers will indicate that difference on
datasheets, catalog listings.

Extended-foil construction offsets the layering so that one foil
overlaps the insulating film or paper at one end, the other foil
overlapping the other end. When axial leads are attached, the
foil overlaps is crimped down on the lead so that nearly all turns
of the foil at one end contact the lead. Minimum inductance.

Conventional old style of construction had the two foils neatly
aligned with no foil protruding from the wider insulating layers.
Axial leads were then clamped at only one end of the foil wrap
end (usually the finish end) and the result had a fair amount of
residual inductance in the remainder of the foil wrapping.

A few makers introduced deliberately series-resonant bypass
tubulars many years ago, intended for the ubiquitous 455 KHz
IF amplifier stage bypassing. Broad series resonance but it
worked (sort of). Rather a rare tubular now. Curiosity.

Len Anderson
retired (from regular hours) electronic engineer person