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Suflex Axial caps

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Suflex Axial caps

Post by crustytv » Tue Sep 22, 2015 9:53 pm

Continuing my Workshop tidy and cataloguing I came across a box of NOS Suflex caps. Various pF values but no voltage refs which is a real pain. I would guess from various small sizes min 30v max 63V. Anyway that's not the query, what I'm curious about is is would anyone know the significance of one end being Red? My gut tells me this might denote outside foil which would make sense if these were to be installed in IF stages.

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Re: Suflex Axial caps

Post by nuvistor » Tue Sep 22, 2015 10:16 pm

Outer foil is what I remember the red is for.


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Re: Suflex Axial caps

Post by sideband » Wed Sep 23, 2015 8:35 am

Yes that's right Chris. These were used prolifically for IF decoupling in (mainly) transistor IF stages. Most had voltage ratings of between 63 and 125V. There were some larger ones with higher voltage ratings and I've come across those in some TV sync circuits.

Mostly they were very good with extremely low leakage (measure a few on your bridge) and close tolerance. You could also find them in tone control circuits and detector stages in valve equipment.

I don't know if any of the markings relate to a working voltage...I've never seen any charts for these. I have a drawer full of these and some are marked with a voltage and some not. All the really small ones that are marked seem to be 63V.

So outer foil is the earthy end when used as decoupling.

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Re: Suflex Axial caps

Post by Cathovisor » Wed Sep 23, 2015 9:02 am

The place I remember them most was in video equalisers.

Some explanation in this datasheet here. (links to LCR website).

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Re: Suflex Axial caps

Post by Valvebloke » Wed Sep 23, 2015 9:31 am

My experience of these has been good too. They seem to be nicely stable. The only thing you have to be careful of is that the leads aren't secured really strongly into the body of the cap. If you pull them too hard they will come out (voice of experience :ccg ).


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Re: Suflex Axial caps

Post by turretslug » Wed Sep 23, 2015 5:59 pm

Reckoned to be stable and low less with (low and predictable) negative tempco but ISTR operating temperature often quoted as only 70 Celsius max, which might sound good but some valve kit could come close after a few hours. Also easily melted by soldering for too long or too close to the body (How do I know that :bba ), I suspect that is why the leads tend to be very thin. This thin-ness means that they need careful handling when fitting and they can corrode through with long-term poor storage.

Worth hanging onto, not so prolific nowadays.

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Re: Suflex Axial caps

Post by Marconi_MPT4 » Wed Sep 23, 2015 8:18 pm

I remember these being used in GEC 2040 series colour decoder circuits. Frequently a no colour fault was traced to one of the reference oscillator capacitors going intermittent as connecting wires would detach inside the case and drop out! It does appear though these capacitors were designed for oscillator circuits as the temperature coefficient is -150ppm per degree C.

Specification for the Suflex HS series polystyrene capacitors:

Suflex polystyrene capacitors show good capacitance stability, low power factor, and high insulation resistance. Generally available in four voltage ratings of 30V, 63V, 160V, and 630V in tolerance of 2.5% to 10%.

Insulation resistance: >10 Gohms
Power Factor: better than 0.0005 at 1MHz
Capacitance stability: approximately 0.3% (over 2 years?)
Temperature coefficient: -150 parts (+/-60 parts per million) per degree C
Temperature Range: -40 degC to +80 degC
Proof Voltage: 2 x Rated Voltage

Colour voltage Note
The 7mm types are marked with capacitance and tolerance e.g. 150/2.5 is 150pF +/-2.5% tolerance
Colour voltage: Blue = 30V, Orange = 63V, Black = 160V, Red = 400V, Green = 630v

Chris, your capacitor is 400V. Not specified but reasonable to expect it also denotes outside foil end.


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Re: Suflex Axial caps

Post by Rallycoordinator » Mon Sep 28, 2015 9:58 am

Valvebloke wrote:The only thing you have to be careful of is that the leads aren't secured really strongly into the body of the cap. If you pull them too hard they will come out. VB

Also care is needed not to apply too much heat when soldering or the leads will become quickly detached - I found this out when constructing a Sinclair Micromatic radio kit in the 1960s.


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Re: Suflex Axial caps

Post by Herald1360 » Tue Sep 29, 2015 12:12 am

ISTR the polystyrene sheet for the dielectric is no longer made.

For low values, NP0 ceramics seem OK. I guess PTFE would be good too.

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