Replacing wax capacitors?

[Stylo N M]

After reading quite a bit recently about the Bush DAC90A radio, I just wondered what other members thought, is it now really time to change those wax capacitors?

All of my DAC90A radios have worked on their original waxies up to now, apart from the change on sight ones ie: "that capacitor", the mains filter capacitor, and tone correction capacitor, It's quite some time ago since I've had chance to fire them up, so I was just wondering, would it be advisable now to start and replace them? They are now getting on for being 68 years old.

Thanks, Paul.

[GMB]

I suggest you look at the circuit and imagine a resistor in parallel with each and ask the question "does it matter?". If yes then action is needed.

So it is capacitors that are blocking DC where it really matters - like between an anode and a grid. Leakage there is really bad, and easily checked by measuring the grid voltage.

Then there is decoupling, where the leakage is just lost electricity - but there is a heating effect and this will eventually become serious too.

Anything connected with the mains needs to meet modern standards (X or Y class) so always replace.

By the way, they will all be leaking to some extent.

[stevehertz]

Yes, 100%. Just change them all. Job done and the set will thank you for it!

[Stylo N M]

Thanks GMB for the suggestion, i hadn't thought about looking at it like that, good point.

Thanks steve for the reply, i shall bare it all in mind any advice members suggest, it is all very much appreciated, thank you.

Paul.

[paulsherwin]

Opinions do differ about wholesale recapping, but I would always do it with a radio of this type and era. It's actually an easy job with a DAC90A as most of the caps are neatly laid out on a tagboard in one place.

[Stylo N M]

Thanks Paul, that's exactly it. I hate blanket changing capacitors if it can be avoided, apart from the usual suspects. It's difficult to know where to draw the line when stuff gets really old.

Paul.

[AC/HL]

It's one of those "lock 10 Engineers in a room" questions. The purists will leave everything "original" and just admire it for it's historical perspective. If you want it to work, then you have decisions to make. Some are no-brainers such as the euphemistic "That" capacitor. Others depend on your attitude to performance, reliability and risk.

[Stylo N M]

Thanks Bill, yes that's very true opinions certainly do differ.

Paul.

[David G4EBT]

Waxy paper caps are known to become leaky over time, they're cheap to replace and on the DAC90A are easily accessible. Given that the DAC90A - though being live chassis is not the best choice for a first restoration - they often are and seem to have a certain appeal. That being so, novices are unlikely to be able to discern which caps (anode to grid etc) are best changed or could be left in place, and are unlikely to have high voltage leakage testers to check them anyway.

The older and rarer a set becomes, the greater the need to consider 'conservation', rather than 'restoration'. The DAC90A isn't rare - it's a commonplace set rented out in their thousands over several years. They're never going to become an heirloom, so conservation isn't an issue, tut it's seventy years this year since they went into production, so the aim is surely to restore the set to perform reliably into the future. That being so, it clearly makes sense for the small amount of time and expense involved to replace all the waxy caps.

Some will argue that this isn't 'proper diagnosis' and the term 'painting by numbers' has been mentioned. I disagree - it's an informed judgement based on the known deterioration of such caps over time. If not leaking now, they may, and probably will, before too long.

Out of curiosity, when I've replaced waxy or pitch covered caps, I've tested the old ones after removal on a Victor VC60B insulation tester. As often as not, even at 1,000 Volts they've shown no leakage. But suppose I'd tested them before with the same results and had left them in place - would that have been a 'proper diagnosis'? I don't think so. Ceramic and mica caps yes - but not waxy paper ones. Why would I leave them in place - to save a fiver, or an hour's work? How would that make any sense? It's an old radio - not a stained glass window in York Minster.

Leastways, that's how I see it.

Resistors are a different matter - most were originally +/- 20% tolerance, just a few were 10%. Unlike caps, they're easily tested.

Worth repeating perhaps that when replacing the caps on the tag-board, rather than unsoldering the ends from the tags, it's much neater and causes less disturbance to clip the old caps out, then rather than re-use the same outer tags, to bend up the unused ones that are flat against the Paxolin, scrape any tarnish off them with a craft knife and solder the new caps to the 'new' bent up tags.

The picture isn't too clear, but the sketch shows what I mean.

[Stylo N M]

Thanks David, well anouther absolutely fantastic write up dave. It always stuns me at the amount of thought and dedication, that's given by members on here, to help people like myself.

Thank you for posting those pictures again dave.

Paul.

[stevehertz]

Originally Posted by Stylo N M

Thanks Paul, that's exactly it. I hate blanket changing capacitors if it can be avoided, apart from the usual suspects. It's difficult to know where to draw the line when stuff gets really old.

I'm defo NOT a blanket changer of caps, especially electrolytics in vintage hifi where there's a US trend to change them all. On the other hand, over 40 years working on vintage wireless sets has shown, nay proven to me that given how most wax paper caps have resistance in varying degrees, messing about trying to ascertain which ones may be 'acceptable' is frankly a waste of time. Hence with waxies I always break my own rule and change them all. At that point a large percentage of possible faults are simply eliminated.

[ms660]

When I was in the R&TV servicing trade there was the bathtub curve.

Lawrence.

[paulsherwin]

Most (though not all) would agree that Hunts Mouldseals are change on sight components now. They will often disintegrate when touched.

[Stylo N M]

Hi Steve, yes I knew exactly what you meant and that's very true, I've found changing electrolytics in vintage transistor equipment seems to change the tone of the amplifier (usually for the worse).

Going back to the waxies, they can be a nuisance, especially in battery valve portables, they seem to be all as high as a kite in those jewel case radios.

Paul.

[paulsherwin]

Waxies will read high on a tester if they are leaky.

[Stylo N M]

They certainly do Paul, especially the little ones.

Paul.