Hunts capacitors - always bad?

[ms660]

Originally Posted by factory

Google books refuses to show the pictures to me, stating copyrighted. And looking on World Radio History for the Vol 68 No. 1 Wireless World (Jan 1962) I suspect some of the advert only pages are missing.

They often are missing but as a first guess for those capacitors I would say 1961-62 ish.

Lawrence.

[GMB]

Oh dear, sounds a bit borderline, although if that was when this range came out the question is then how long were they being made?

There are some more modern-looking resistors which are banded 1%. That was not so common in the 60's I seem to remember.

Paper capacitor life is all about the quality of the paper used, but I had hoped these could be something more modern. It might be interesting to study their exact performance. I strongly suspect that the paper decomposition reaction that generates the water that messes them up is auto-catalytic so I would expect to see an exponential death spiral. I will have to do some more precise measurements.

I presume that no-one has encounted these particular capacitors before?

[McMurdo]

Plenty of hunts capacitors still in use in this neck of the woods as power-factor correction in fluorescent lights. I've had the dubious honour of being covered in wax from an overheating venting hunts in a light fitting where I used to work one hot sticky afternoon.

Modern PFC tubular capacitors have plastic ends that are made to blow-out and disconnect the power if they explode. So they haven't cured that little problem just yet!

And the Queen Mary 2 has had its fair share of 'modern' capacitor problems, so give the poor old Hunts a break!

https://assets.publishing.service.go.../QM2Report.pdf

[ms660]

Here's another type number using the same encapsulation style:

https://vintage-radio.net/forum/showthread.php?t=74657

Lawrence.

[Nuvistor]

Originally Posted by AC/HL

If it is or contains paper it's suspect, in direct relation to it's original budgetary roots. Economy ones failed long ago, better ones may linger on for a while. In relation to market share they were probably no worse than average, it was the technology that had inherent limitations.

I think that sums it up very well.

[Heatercathodeshort]

Originally Posted by Richard_FM

Callins is another brand of components that doesn't seem popular in certain circles.

Again to be fair to Callins, the electrolytic type that were a known failure and replaced on sight are the black plastic encased ones with the red seal. They were extensively used in Thorn chassis particularly the 2000/3000/1400/early 1500 going S/C or developing heavy leaks.
They were not made in the USA but a lot nearer home. Callins produce high quality capacitors but something in the design of these particular types caused very early failure. It was a long time ago [1960s early 70s] and a lot of water has run under the bridge.
John.

[AC/HL]

Economy packaging again. You always get what you pay for!

[Richard_FM]

Originally Posted by Heatercathodeshort

Again to be fair to Callins, the electrolytic type that were a known failure and replaced on sight are the black plastic encased ones with the red seal. They were extensively used in Thorn chassis particularly the 2000/3000/1400/early 1500 going S/C or developing heavy leaks.
They were not made in the USA but a lot nearer home. Callins produce high quality capacitors but something in the design of these particular types caused very early failure. It was a long time ago [1960s early 70s] and a lot of water has run under the bridge.
John.

OK I see.

[Lucien Nunes]

So still no idea on the date of them?

@trobbins made a foray into this in post 2, but the plot thickens. Date code is 3 capital letters at bottom of print block. The only code I can read completely, I agree is HIN, which decodes to 237. There are at least two ways to interpret that: Week-Week-Year and Year-Week-Week. The transition between schemes was around mid 1966.

The capacitors do seem like 1960s parts but that doesn't work with HIN. When interpreted by the pre-1966 method (WWY) it yields week 23 of 19x7, but interpreted by the post-1966 method (YWW) it yields week 37 of 19x2, so neither appear valid for the 1960s. The inference is that they are either 1957 or 1972. Erie, who took over Hunts around 1970 IIRC, carried on using the Whitsunday code briefly before switching to YYWW numeric codes, but I don't know when they stopped branding products 'Hunts.' I think it is at least possible that they are 1972.

Then there is one with a partially visible code ?DY, which decodes to ?80. As there is no week 80, this must be WWY which implies 1960 as WWY was not in use in 1970. It's unlikely that the two capacitors would be 12 years apart but two or three is plausible. Could they really be 1957 and 1960 respectively?

Can you read and post codes from the other caps? I'm determined to get some more mileage out of the effort that it took for the team to crack the code!

[dazzlevision]

The Erie UK catalogue of 1973, after they had acquired Hunts, does have a section on the 53205 series (previously known as WF312 series) and specifically the part AF227 (0.15uF, 600Vdc working, 20%). It also says the range will be withdrawn on 30th June 1973. So, clearly an obsolescent product.

They are called Duolectric "Supermoldseal" metalled paper & film capacitors.

Construction: metallised lacquered paper and Polyester film interleaving, enclosed in "Supermoldseal" cast epoxy resin.

Insulation resistance: 0.05uF and below: >25GOhm
above 0.05uF: >2000OhmF

Temperature range: -55C to +100C

Dissipation factor: < 0.02 at 1kHz at 20C (+/- 5C).

[GMB]

Originally Posted by dazzlevision

The Erie UK catalogue of 1973, after they had acquired Hunts

Significant, as I had not noticed that some of these capacitors are marked ERIE (not the ones in photo). They look the same at first glance but are slightly different shade of blue.

Survey of codes:
ERIE codes are IDY, IAA, YII

HUNTS codes are HHH, HIN, YSI, YII, IDY

I think this may be suggesting which one I need to carefuly test?

So is this putting it firmly in the 1972/73 range?

[stevehertz]

Those small, tubular Hunts caps that were encased in a dark, almost black and sometimes brown plastic were prone to the casing going brittle and falling off. Was this the cause of them going faulty ie moisture ingress, was it symptomatic ie a consequence of what was going on inside, or pure coincidence ie just another example of how poorly they were?

[GMB]

Originally Posted by stevehertz

Was this the cause of them going faulty ie moisture ingress

No.
The moisture ingress often quoted is a popular assumption and obviously can be a problem, but there is definitive evidence that this is not the primary cause of failure. We know they fail in spite of being sealed in bomb-proof military hermetic cans so moisture ingress can't be the reason.

Paper capacitors fail because the paper decomposes liberating water in the process. This happens because of the way the paper is made. Look at cheap paperback books that are a few decades old and you will see that the paper is turning brown, almost the same as if it was heated to a high temperature. Now look at high quality books that are much older - and you soon see how widely the quality of paper can be.

I am always interested in the state of capacitors and their age as I am trying to investigate the rate of decomposition. My gut feeling is that this is an auto-catalytic process as I get the impression that they remain fine for years and then quite quickly deteriorate.

[Lucien Nunes]

So they are mixed dielectric types which might read OK to a DC insulation test on account of the polyester, but have degraded performance and possibly drifted capacitance on account of the paper. Do they read high in value?

A couple of those codes have broken the system. IAA = 399 which cannot be (YWW) or (YMM) so it seems the (WWY) scheme resumed or was never changed for some products. And as it is branded Erie it has to be 1969. I need to re-visit the misfits from the previous investigation...

[stevehertz]

Originally Posted by GMB

No.
The moisture ingress often quoted is a popular assumption and obviously can be a problem, but there is definitive evidence that this is not the primary cause of failure. We know they fail in spite of being sealed in bomb-proof military hermetic cans so moisture ingress can't be the reason.

Well the plastic outers of those small Hunts caps that I refer to certainly aren't bomb proof, the plastic outer just crumbles and falls away as soon as, or even before you touch it. The brown or black ones in the photo.

[Lucien Nunes]

I think the point here is that all paper capacitors other than some oil-immersion types are ticking time bombs due to the self-destruct mechanism of the dielectric, regardless of whether they are in hermetically-sealed cans or at the mercy of the weak and short-lived Moldseal encapsulation. All the inferior Moldseal material did was to hasten the decline. It might be true to say that the encapsulation was mainly responsible for the bad reputation that Moldseals gained during their service life, but their condition now is as much due to them simply being paper types.

@Stevehertz do you still have the RTC and Erie caps in that pic, and if so could you possibly post the date codes please?

[G6Tanuki]

Yes, the Metalmite/Metalpack Waxies-in-a-shiny-aluminum-case (fitted to loads of Military gear in the 50s/60s) are just as disastrous; If you find these in a coupling/decoupling or AGC-line application... unquestionably - rip them out and fit something non-leaky [my go-to are Vishay yellow polyesters].

Life's too short to be spent chasing-down faults caused by 60-year-old waxies.

[G6Tanuki]

Though Hunts are not always bad: I have a 300pF 2.5Kv Hunts ceramic 'doorknob' capacitor here - bought for a transmitter ATU project - when threatened with the highest DC voltage I can easily produce - around 1.1Kv - seems entirely leakage-free.

[The Philpott]

I'm certain at least one of my old avometers ('fifties or 'sixties era) has a Hunts cap on one of the resistance boards, very similar to the red jellybean BD603 Steve shows in Post No.35....what is it's function?

Dave

[TowerRadio]

"Call for Hunts!"- old TV advert.Les