MultiCap RTX series parts exhibit very low ESR/ESL. So, inductive destabilization is not a problem. However, along with the substantial cost, polystyrene film is sensitive to heat. The environment near power O/P tube types is usually quite hot.
IMO, polystyrene dielectric caps. are best saved for use in comparatively cool environments. That's not a happy decision, when the fact that only PTFE is more transparent than polystyrene is taken into account.
IMO, polystyrene dielectric caps. are best saved for use in comparatively cool environments. That's not a happy decision, when the fact that only PTFE is more transparent than polystyrene is taken into account.
I used MIT and then REL RTX (polystyrene and foil) caps in my power and pre-amplifiers for years, and thought they were great until I heard some similar Teflon types which were clearly better. I thought the RTX were a bit bright sounding, but in terms of resolution were better than the CDE and Mallory film caps I had used previously, and also sounded much cleaner as if a layer of grunge had been removed.
I never had any heat induced issues with these capacitors, I just found something I liked better.
These days I use mainly Vcaps, REL TFT (Teflon), one of the various surplus Russian made Teflon coupling caps people have raved about or transformers.
All good.
I never had any heat induced issues with these capacitors, I just found something I liked better.
These days I use mainly Vcaps, REL TFT (Teflon), one of the various surplus Russian made Teflon coupling caps people have raved about or transformers.
All good.
Re: plystyrene is inductive ?
Hi,
Polystyrene are leaded at opposite ends and rolled while polyester and polyethylene are rolled then have the leads welded, eliminating the inductance.
Take a look at the (axials show this best) polystyrene caps in a tape recorder or RIAA stage. Notice the leads are offset?
I've neasured as much as 20uH inductance on a new manufacture 3000pF polystyrene cap. A coupling cap like you're talking about, say 0.1uF, could be has high as 100uH.
Because they are used in stages like RIAA or precision timing or bias oscillators where a few tens uH in line is moot for the impedance levels involved.
I'll have to check those out Eli, thanks for the heads up!
x2. I forgot about that fact.
Cheers!
Hi,
aldovan said:
Polystyrene are leaded at opposite ends and rolled while polyester and polyethylene are rolled then have the leads welded, eliminating the inductance.
Take a look at the (axials show this best) polystyrene caps in a tape recorder or RIAA stage. Notice the leads are offset?
I've neasured as much as 20uH inductance on a new manufacture 3000pF polystyrene cap. A coupling cap like you're talking about, say 0.1uF, could be has high as 100uH.
aldovan said:
Because they are used in stages like RIAA or precision timing or bias oscillators where a few tens uH in line is moot for the impedance levels involved.
I'll have to check those out Eli, thanks for the heads up!
x2. I forgot about that fact.
Cheers!
I have recently started using polystyrene/tin foil couplers in my power amps. They have a combination of transparency to fine detail and tonal richness I have heard in nothing else. Mind you, I have not tried the megabuck teflon caps. They are not terribly expensive, but they are big and heavy enough to be a mounting problem, and do not come in high enough values for my preamp output.
Poinz likes 'em.
Aloha,
Poinz
AudioTropic
Poinz likes 'em.
Aloha,
Poinz
AudioTropic
Re: Polystyrene is more inductive ?
Regardless of construction similarities or differences polystyrene is a far better dielectric than polyester. (DA/DF) It's quite audible which is why of all of the plastic dielectrics I now prefer teflon even to polystyrene which was my preference for about 15yrs or so. Exotic teflon types are just so expensive which is why I waited so long to make the switch. Other than the eq caps in my phono stage every coupling cap in my system is now teflon. (Exception: The X-O caps in my system are polypropylene foils and are the best I can "currently" afford.)
aldovan said:
Regardless of construction similarities or differences polystyrene is a far better dielectric than polyester. (DA/DF) It's quite audible which is why of all of the plastic dielectrics I now prefer teflon even to polystyrene which was my preference for about 15yrs or so. Exotic teflon types are just so expensive which is why I waited so long to make the switch. Other than the eq caps in my phono stage every coupling cap in my system is now teflon. (Exception: The X-O caps in my system are polypropylene foils and are the best I can "currently" afford.)
MRupp said:
"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.)
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