Polystyrene capacitor as coupling in output tube stages

[kevinkr]

Originally posted by MRupp


There are obviously 2 types of polystyrenes, the "laid-in" type with the connectors wrapped in with he foil, and the "extended foil" type where the leads are welded to the foils at both ends of the cap, much in the same way as other types of capacitors.

"Laid-in" types are common below 10nF/0.01uF and "extended foil" types are relatively standard for higher values (in the USA anyway) and types that are deliberately intended to be low inductance like the RTX. FWIW I have never found inductance to be a particularly big issue with foil types in most circuits - input impedances to succeeding stages are usually high enough that the inductive loss term is irrelevant at audio frequencies - and in any event are still likely to better than most other types other than clearly audio unsuitable ceramics and micas. (Some Russian micas are reputedly quite good for audio, but I have not yet tried these.)