Wax capacitors - what's your approach?

[stevehertz]

(Moderators, I ticked the box for this to be a poll, but as I now look at the preview it doesn't appear to be formatted as such?)

When a set you're restoring has wax paper capacitors, what is your approach to dealing with them?

1) Change every one on sight, no testing.

2) Test each and every one out of circuit (one end snipped) and replace it if faulty.

3) Leave them all in place and change as when you find them to be the cause of an operational fault.

4) Change ones known to be fitted in a problematic or potentially dangerous circuit position, but change others as and when found to be operationally faulty.

[Station X]

I've added a poll for you, but had to edit option 4 as it exceeded the 100 character limit.

[Dave Moll]

I assume this is referring specifically to the waxed type of capacitors with a paper dialectric as opposed to the wax-covered capacitors (usually in the form of a flat square) with mica dialectric.

I tend to change the former on sight, replacing them with equivalent polypropylene ones. These are usually in the form of a yellow cylinder that, to my eye, doesn't look too out-of-place as a substitute.

[stevehertz]

Originally Posted by Dave Moll

I assume this is referring specifically to the waxed type of capacitors with a paper dialectric as opposed to the wax-covered capacitors (usually in the form of a flat square) with mica dialectric.

I tend to change the former on sight, replacing them with equivalent polypropylene ones. These are usually in the form of a yellow cylinder that, to my eye, doesn't look too out-of-place as a substitute.

Dave, as specified, waxed paper.

[Station X]

My approach is to change the audio coupling capacitor before applying power.

I then carry out normal fault finding identifying faulty capacitors and replacing them as necessary. This helps maintain my fault finding skills.

Then, once the set is working I change all the waxed paper dielectric capacitors one at a time, retrying the set after every change. This prevents fitting a component of the wrong value in the wrong place.

I've never repaired a set where where simply replacing all the capacitors restored operation, there were always other faults which had to be found using normal fault finding procedures ie using a meter.

I've seen plenty of threads of the form "I've changed all the capacitors and it still doesn't work". Often this literally means ALL the capacitors including silvered mica and ceramic types which seldom need changing.

I would also add that it's seldom necessary to snip one end of a capacitor in order to test it. With the exception of cathode capacitors in output stages most wax capacitors in domestic sets are not shunted. Also the only sure fire wire of testing capacitors is at their full working voltage.

Some members with hundreds of posts to their name appear to have little technical knowledge, never seem to acquire any and try to get by by changing components because the LOOK faulty.

[GMB]

I would also add that it's seldom necessary to snip one end of a capacitor in order to test it. With the exception of cathode capacitors in output stages most wax capacitors in domestic sets are not shunted. Also the only sure fire wire of testing capacitors is at their full working voltage.

I would go further to say that if a non-electrolytic capacitor cannot be leakage-tested because there is something bypassing it then it probably doesn't matter (much) if it is leaky.

I always look at exactly what each part is doing and decide whether leakage matters in its case. This usually means that most capacitors do not need changing. The only time I ever changed almost all the high-value paper-type capacitors in a set was on AN/APR4 where the misleadingly named "Micamold" capacitors (no mica involved) were all in a totally dreadful state with leakage that even an AVO could easily spot.

If the set is worth keeping original I will try cooking paper capacitors under vacuum to restore them back to health.

[Lloyd 1985]

I picked option 4, I always like to see if an item can work with all its original components before replacing anything, especially if it’s an item with a lot of parts that could potentially need changing, it’s always worth making sure the item in question is basically functional before blowing a load of money on replacement caps just to find that said item has an O/C transformer, or in the case of a TV, a duff tube.

I’ve just got myself a Marconi R1155, And there are a lot of caps in that! I’ve had it running before restoration, just to see if it would work at all, and to my surprise it does! With the HT wound up the stations begin to fade, and some of the caps begin to protest by getting warm or oozing goo, so they get changed first.

Regards
Lloyd

[HamishBoxer]

Grahams approach is what I use, of course if I see a smoothing capacitor that is burst,t hen I would change on sight or re-stuff. Though brown/black Hunts are straight out.

Depending where they are in the circuit it would be rare to change all. Things like the AR88 cap that goes from primary o/put tx /anode connection to earth, I would not think twice about changing. Of course that would on those be rewired across both primary connections.

Re stuff by all means if it is a rare set/equipment.

[ThePillenwerfer]

Change the lot.

[Leon Crampin]

I give the highest priority to safety and the limitation of consequential damage to equipment.

So, aerial/earth isolating capacitors are replaced, as are AF coupling capacitors and half wave rectifier RF bypass devices. Others are judged on merit - for instance a 100 nF wax capacitor shunting a 150 ohm cathode bias resistor in an IF amplifier would probably be left alone. During alignment, I might temporarily shunt it with another, just to check that it's doing its job. Tone correction capacitors wired across the output transformer primary can also generally be left - but definitely not those wired anode to ground.

There is some merit in keeping the old wax cases though. Resin dipped radial capacitors are cheap - axials are not. When restoring a KB FB10 recently, it was far easier and better looking to keep the 50 nF capacitor wax cases and slide in a 47 nF 630V resin dipped radial replacement. I don't seal the ends - it just sits in there looking original and safe.

To complete - electrolytics I take on merit. Generally, pre-war components have to be changed/re-stuffed. Post war, it depends on make and condition. BEC (British Electric Condensers) components in Al cans as used by Bush are nearly always OK, as are the earlier Plessey devices (because Plessey bought BEC). Bulging devices or those with perished bungs need to go.

Leon.

[paulsherwin]

I change all waxies and Mouldseals between 0.001uF and 0.1uF. There's no point in testing them because they *will* be bad. Yes, sometimes a leaky cap won't affect circuit operation, but by not changing it you are knowingly leaving a faulty component in place. Leaky caps can cause all sorts of strange symptoms and make fault finding much more difficult.

Changing caps proactively is no substitute for proper fault finding of course, and many beginners do change caps in the naive hope that this will cure some fault. They even change types which are very unlikely to be bad, such as micas or ceramics.

[Dave Moll]

Originally Posted by stevehertz

Dave, as specified, waxed paper.

Sorry. I missed the inclusion of "paper" within the OP.

[Radio Wrangler]

Replace the audio coupling capacitor, then try a little power just to get a quick assessment. Say 'what the hell' and replace all the other paper capacitors, mouldseals, hunts, waxed, 'micamold' whatever.

I'll leave waxed mica alone. They're usually OK.

Things like the Marconi stud-ended paper decouplers I might restuff, same for bathtubs.

David

[Refugee]

I often put rectified isolating transformer output with a limiter resistor on the HT and measure the control grid voltages and only power the unit up if they look "reasonable".
Apart from output stages most can be left until the set has seen full power.
You get the odd one decoupling low signal circuits that can kill a resistor however these can be found with the external DC check saving lots of work.
I will eventually change all of the ones that run more than about 70 volts.

[G6Tanuki]

I change-on-sight, for several reasons.

1] It takes about as long to 'lift' one end and test the capacitor than it does to lift both ends and replace with a new one.

2] Following on from [1], the majority of waxies I've found _will_ be defective.

3] If they're not defective now chances are they will be in the next couple of decades.

4] I like my equipment to be safe and reliable - if I can't safely leave it powered-on unattended it has no place in my shack, or anyone else's house.

[stevehertz]

My thinking, to the word.

[Sideband]

I chose option 1 for radio's. However with TV's I would choose option 4.

[Ian - G4JQT]

If you want to use the radio/TV/amp, change the lot. Those across cathode resistors can probably be left as they are already across a relatively low resistance. Nevertheless, I'd still remove them - they're not going to improve with age.

[Station X]

Replacing capacitors on sight is fine for experienced repairers/restorers, They're unlikely to fit the wrong value component in the wrong place. If they do manage to do this, let's face it we've all done it, they're likely to be able to sort the problem out by looking at the service sheet, checking voltages etc.

Where newbies are concerned I'd recommend a much more cautious approach as some of them have little technical knowledge. Look at the number of queries we get of the form "What do I replace a 0.5uF capacitor with?" or sometimes just posting a picture of the component in question. Many of these queries come from repeat offenders who never seem to learn anything.

I always reach for the test meter before I reach for the soldering iron.

[kalee20]

All the options for me really - ideally replace the lot. If I want to get something working, and I know it has recently been powered-up anyway, I'll leave in place and change as I find problems. Which often is a case of snip one end, test, if OK blob of solder over the snip; if not OK, replace.

I'll always change 'that' capacitor, given time, as consequences of leakage are rather significant.

And doing a thorough job, as I say, it's change the lot.