Dubilier capacitors

[ScottyH]

Hi all,

Does anyone know where I can find replacement capacitors like these Dubilier capacitors pictured?
I'm assuming they are oil filled, but I can't find anything with this voltage rating.

I can only reform to 500V ish, no where near 3.5KV...

The other photo has a mix of capacitors, the Hunts is shot, as is the gold micropack electrolytic, but I'm curious about the small blue caps at the bottom and the plastic Hunts at the right.

Replace outright?

I'm guessing polyester replacements would suit here, if I can find the correct voltage rating.

Any advice appreciated.

[lesmw0sec]

My first question would be as to whether you really need 3.5 KV? What is the kit it is fitted to?

[ScottyH]

There are three of these on the output of two EY86 tubes providing HV for an oscilloscope. I’m assuming that these are original and not replacements. Unfortunately I don’t have a schematic.

[lesmw0sec]

Ah that makes sense - it looked like it might have been an audio amp where someone had fiited the cap as it was 'to hand'! I would have thought that in general, polyester would be fine for the rest, but can't suggest a source for the higher voltage ones. If they are oil filled though, it is quite possible that they are blameless if not measuring any leakage.

[ScottyH]

They don’t seem to be leaky, but as I can only test to 500v or so who knows?

[joebog1]

The BIG give away with high voltage EHT caps is that the trace will be "blurry" till the caps reform.
I have a wonderful old scope that works fine, BUT takes 20 minutes to have the focus control working.
I put up with it because everything else "works like I remember".
ALL else is probably crook too, BUT I soldier on.

VERY hard to find new exact examples, BUT there are some very good polyester hi voltage caps that will serve.
Joe

[ScottyH]

Thank you, in that case i shall stick with them as they are.
At this stage the HV is missing, but once the other pesky caps get removed things can move forward.
(School holidays at the moment, so time spent on anything is biased toward the lads.)

[FrankB]

RF Parts,
https://www.rfparts.com/old_site/index.html
Is a good source.
I bought a quantity of HV 'lytics from them for replacement in early TV sets and 'scopes.

Honest and nice folks to deal with. They are one of the few companies left that carry stuff for the ham equipment.

[ScottyH]

Perfect. I’ll have a look. Thank you.

[Craig Sawyers]

What an excellent shop. Why is this sort of great place inevitably in the US? Why are we incapable of this in the UK?

Craig

[MrBungle]

Also worth looking at http://hvstuff.com/ . I've ordered from them a few times. Takes a couple of weeks to turn up as it's shipped from China I think but the parts are usually top notch.

[Uncle Bulgaria]

Originally Posted by Craig Sawyers

What an excellent shop. Why is this sort of great place inevitably in the US? Why are we incapable of this in the UK?

Craig

Possibly population size and demand. Despite being more concentrated in the UK we are far less willing (probably a good thing we're not as car-centric) to travel long distances for things. It always seems to crop up in online discussions that Americans go down the road and buy gallons of a particular chemical, or great quantities of hardware or specific components while we're stuck with Wilko or if you're lucky enough to have a hardware shop, those plastic packets of flimsy 'Home Hardware'.

RF Parts looks excellent. A bit Electrojumble (has anyone heard from Roy? The site's been down for a long while) and a bit Partridge Electronics. Just how I like it!

In NZ, Element 14 (Farnell in the UK) has some 3kV 0.15µF film capacitors...made by Cornell Dubilier!

However, as Joe says if they're working and not leaking, then they're probably fine. I'd replace them if there's a problem when you've put the rest of the power supply back together.

[ScottyH]

As I’m currently stuck on a beach in Waihi, I’ll have to wait to get home to look further. I found a post last night about building an HV cap reformer that plugs into one of the rectifier tube sockets, effectively using the sets own transformer to gently reform the capacitors. It looks like a great way to check the whole circuit out.
If they work out to be faulty the responses to my question have given me more than enough information to source replacement capacitors. Thank you.

[trh01uk]

I am unclear that the capacitors here can be "reformed". This process refers to rebuilding of the insulating layer in an electrolytic capacitor. Some of the capacitors here are unlikely to be electrolytics - the Hunts one in particular are more likely to be paper. For those polyester replacements should be fine, and easy to find.

I am unclear on the Dubilier one, at 0.15uF at 3.5kV. There's nothing I can see in the photo to indicate its an electrolytic, so reforming it won't arise. If it's leaky - and you can check that OK at 500V - then it will replacing.

Richard

[ScottyH]

Thank you Richard, you are correct.
There are electrolytic caps in there, and I’ll just replace them, as I will with all the paper ones.
The big 3.5KV caps will just have to be checked, not reformed as I said earlier. (Holiday brain engaged. )
Hopefully they will be OK.
Scott.