U67 capacitors -- need help

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I have a '62 U67 that I have refurbished with a new k67 capsule (I
kept the old one as-is and bought a new one from Neumann).
The circuit uses negative feedback and the signal passes not only
through the electrolytic coupling cap for the primary of the
transformer, but feedback passes through a few .01 WIMA tropyfol
(anyone know the modern equivalent) capacitors and high frequency
feedback passes through a Styroflex (anyone know if this is
polystyrene??) 80 pF cap.
I am going to replace the 40 year old electrolytic and keep the
original for an eventual sale of the mic (for those who love old
capacitors).
This kind of circuit is very sensitive to phase shifts etc. so I am
hoping that the mic will improve once I re-cap.

My question: do the foil WIMA caps in the mic and the Styroflex cap
change as they age?
I know electrolytics and paper change but have no experience with the
ageing of plastic/foil caps

Can anyone offer help??

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey <kludge@panix.com> wrote:


> did perform well when they were new). Electrolytics are really the only
> capacitors that degrade slowly as they age.
> --scott

Is that simply because as the electrolyte gradually dries out they become
less efficient conductors?

Does this mean that all "solid state" capacitors do not periodically need
to be replaced, and should only be replaced after failure, or for an upgrade
in quality?

I have heard some people suggest that we gone overboard on recapping
equipment. Perhaps a lot of business is being generated by recapping
loder units that really don't need it.

Rob R.

Archived from groups: rec.audio.pro (More info?)

"Scott Dorsey"

>
> >I know electrolytics and paper change but have no experience with the
> >ageing of plastic/foil caps
>
> Paper caps don't degrade slowly, they just fail abruptly.


** Paper caps can become leaky with age due to moisture ingress.


> Electrolytics are really the only capacitors that degrade slowly as they
age.


** In general that is not true.

Electros hold their capacitance value and ESR figure throughout their
ife - only when most of the electrolyte is lost through evaporation the
ESR figure goes high.





............. Phil

Archived from groups: rec.audio.pro (More info?)

"Mike Rivers"
>
Phil Allison:
>
> > Electros hold their capacitance value and ESR figure throughout their
> > life
>
> That's true. It's just that their life is shorter than some other
> types of capacitors.


** More out of context tripe.


Mike Rivers Disease ( aka rampant over snipping) is in epidemic
proportions here.





.......... Phil

Archived from groups: rec.audio.pro (More info?)

<neil.henderson@sbcglobal.netNOSPAM
>
> Good Lord, Phil... give it a rest. Look what you're doing with your
life...
> you're on a one-man mission to discredit a particular individual.


** Rivers came into the thread late and attacked only my post with his
mindless drivel.

Who is the aggressor ???

Who the defender ?




............ Phil

Archived from groups: rec.audio.pro (More info?)

maxdm wrote:

> I have a '62 U67 that I have refurbished with a new k67 capsule (I
> kept the old one as-is and bought a new one from Neumann).
> The circuit uses negative feedback and the signal passes not only
> through the electrolytic coupling cap for the primary of the
> transformer, but feedback passes through a few .01 WIMA tropyfol
> (anyone know the modern equivalent) capacitors and high frequency
> feedback passes through a Styroflex (anyone know if this is
> polystyrene??) 80 pF cap.

'Styroflex' caps are indeed the same as polystyrene.

I recall the WIMA Tropyfol M caps. Without going to the 'archive' I think
they are pretty much similar to today's polyester film types.


> I am going to replace the 40 year old electrolytic and keep the
> original for an eventual sale of the mic (for those who love old
> capacitors).
> This kind of circuit is very sensitive to phase shifts etc. so I am
> hoping that the mic will improve once I re-cap.
>
> My question: do the foil WIMA caps in the mic and the Styroflex cap
> change as they age?
> I know electrolytics and paper change but have no experience with the
> ageing of plastic/foil caps

Generally speaking, relatively modern ( 1970's on ) plastic film types
are unlikely to age significantly.

I have experience however of the old Hunts 0.01uF coupling caps in early
Vox amplifiers. I think these were paper / film ( in a plastic case ).
They degrade physically - as in literally crumble apart after 20 or so
yrs of use !


Graham