NOS 'black' Hunts

[Phil G4SPZ]

I've been given a quantity of 0.5uF and 1uF 250V and 350V black Hunts capacitors. These appear to be new old stock, but have clearly spent many years being bounced around in an engineer's spares box! I have checked some of them and they test perfect, spot-on value and zero leakage on an ohm-meter, although I've not tested them at working DC voltage.

Three questions: (a) are they safe to use in repair and restoration work, (b) would anyone like some, to maintain the original appearance of a set? and (c) do Hunts capacitors deteriorate only when they've been subject to high voltages over years of service, or were they crp from the start?!

Phil

[dave_n_t]

Originally Posted by G4SPZ

questions:
(a) are they safe to use in repair and restoration work,

(c) do Hunts capacitors deteriorate only when they've been subject to high voltages over years of service, or were they crp from the start?!

Phil

Phil,

I've had some NOS Black Hunts caps in the past. I tested them with my (500V) hand-cranked megger, and the vast majority of them showed leakage below 1Mohm - so, not worth using.

(Certainly not as that capacitor; but even as s.g. decouplers they may well pull down the s.g. voltage too much + so cause low gain in the relevant stage).

I think it's slightly unfair to complain about them - they probably lasted far longer than anyone would have expected. (And were almost surely fit for purpose when they were made).

HTH

dave

[Sideband]

You need to check these at something approaching their working voltage. More than likely they will start breaking down at 50 - 100 volts. There is just not enough voltage from a standard multimeter to check insulation.



Rich.

[Tim]

There is just not enough voltage from a standard multimeter to check insulation.

I use a megger to check these.

[Phil G4SPZ]

Thanks for the advice, chaps. I'll try a higher test voltage and measure the leakage current.

Phil

[Hunts smoothing bomb]

Personally I wouldn't use them as (in a sense) its not being subject to voltage that breaks them down, it is the years of absorbing moisture from the air that forms the leak.

Cheers
Lee

[XTC]

It depends where you use them and what damage they can do if they go O/C or S/C or have a level of leakage which might be 25MegOhms but could destroy something you really don't want destroyed.

I'd consider these things to be junk but possibly invaluable to a future rebuilder who wanted some nice examples to mold things around. The fact that we can't buy such caps as new production these days, isn't down to that they were superb, but they couldn't make them cheap enough, it amounts to that there came about better ways of making caps with new materials, and the experience of trying to make caps with paper and wax was painful.

Three questions:
(a) are they safe to use in repair and restoration work,

It sort of depends, but basically no.

b) would anyone like some, to maintain the original appearance of a set?

Yes, but were the set valuable, they would be unwise to assume that even if they appeared good under any reasonable test, that they would remain good,

(c) do Hunts capacitors deteriorate only when they've been subject to high voltages over years of ervice, or were they crp from the start?!

They weren't crap from the start, otherwise they wouldn't have sold. They were trying to do a good job and balancing costs and the risks of using new materials against the expected service life of their caps. Who would have expected anything sold into the consumer market to last more than ten years? Collins used 'Black Beauties' (about the same as your caps) in their very high priced receivers and some owners have found they failed and did in their mechanical fillers on the way out.

I just wouldn't trust those caps with anything important, no matter how they'd been kept or how they tested.

Pete.

[Phil G4SPZ]

Thanks everyone for your responses - much appreciated and some very interesting points made. I am restoring a 0-500 volt DC variable power supply at the moment, and when it's finished I'll test these Hunts again for leakage at their working voltage. As you say, it's probably best to keep them as museum pieces rather than re-use them now.

Thanks again.

Phil

[Phil G4SPZ]

Initial results are encouraging. I tested a 1.0uF 350VW capacitor at 350 volts. Result: after charging, immeasurably small leakage on my 50uA meter. And a satisfying spark on discharging!

When time permits I will test more of them, and compare them with my new stock of polypropylene capacitors to make a 'live' comparison.

However I do appreciate all your comments, and won't be using these Hunts components in restoration work.

Thanks for everyone's interest.

Phil

[Hunts smoothing bomb]

Hi Phil,

Be careful when testing those caps at their WKG volts, if one suddenly goes short it will go off just like a "Standard Fireworks" banger!!

All the best
Cheers
Lee

[Phil G4SPZ]

Good point, Lee, thanks. Although I am charging the capacitors from a very high-impedance current-limited supply, the charged capacitor will store significant energy. I will run a long pair of leads outside into the garden, and place the Hunts capacitor under test inside a strong receptacle in case things go bang

This reminds me of a friend's father who built a Williamson amplifier. His party trick was to casually throw a charged capacitor to someone and say "Catch!" Oh, the things people did before Health and Safety...

Phil

[Hunts smoothing bomb]

Originally Posted by G4SPZ

This reminds me of a friend's father who built a Williamson amplifier. His party trick was to casually throw a charged capacitor to someone and say "Catch!" Oh, the things people did before Health and Safety...

Phil

Quite Phil! It is a shame,

I didn't realise you were using a high impedance source, nothing too dramatic should happen in that case

Cheers
Lee