AR88 Tub Capacitor Oil - PCB's?

[Mark James]

I have recently acquired an AR88. Looking up previous posts etc the tub capacitors which are likely to need replacing are filled with oil. There appears to be some question as to the nature of the oil - an article in Radio Bygones (No. 126) on how to restuff them did not mention any hazards. Before I restuff them can anyone tell me if the oil is likely to contain PCB's?

Thanks,

Mark

[Station X]

The answer is that no one knows. It looked like cooking oil to me.

Just take reasonable precautions when handling it.

If you're restuffing, you can dispense with the rear covers.

[G3PIJpeter]

Clean the end of a piece of 14 swg copper wire with sandpaper. Light a propane blowlamp and place the end of the wire in the blue part of the flame until the wire does not impart a colour to the flame. When cool, dip the end of the wire in the oil and return to the blue part of the flame. If the flame takes on a greenish colour, then you have PCB/PBB oil; if a yellow/orange colour, then you have a straight hydrocarbon (mineral) oil.
This test is a variation on the school chemistry 'flame tests' with a platinum wire and seems OK at discriminating substances that contain chlorine or bromine from those that don't.
- Peter

As Station X said, just take reasonable precautions, it's long term exposure for most of these things that causes problems. On the other hand you may find the caps are fine and even if they are filled with PCBs best to leave it in place.

[Mark James]

Thanks for the information - I like the school chemistry solution! Up until now I knew that they used PCB's in transformers but was unaware that they may have been used in oil filled capacitors. Did they know the risks when they used them?! Are we likely to meet them elsewhere?

Mark

[G6Tanuki]

Originally Posted by Mark James

Did they know the risks when they used them?! Are we likely to meet them elsewhere?

Back in the 1940s and 1950s and 1960s the risks of PCBs were not really appreciated (a bit like Asbestos, Phosphorus, Radium...)

You may also come across PCBs in high-voltage stuff in early oscilloscopes and TVs, like LOPTs, triplers and the capacitors they needed back in the days when the multi-Kilovolt EHT was derived directly from a separate winding on a mains-driven EHT transformer. I believe PCB-containing capacitor/diode "cans" were also used in some of the early (1950s-1960s) microwave-ovens too.

[TonyDuell]

A friend of mine who worked professionally with substation transformers and switchgear gave me the following advice :

"If you work every day up to you elbows in PCB transformer oil then most likely you will get skin cancer. But the amount in one capacitor of the size you work with [meaning as found in radios, TVs, 'scopes, etc] is unlikely to do you much harm unless you are very silly with it"

In other words, yes I do avoid touching it. I do wash my hands after working with such devices. But I feel that worrying about it could be a bigger risk to my health than the PCB oil itself. I just hope that's right...

[Kevin Hoyland]

Hello.
Over the last 6 months I have been working on my 3 Ar88. One is a CR91, one is a 88Lf and the other is a AR88D. I have replaced all the bathtub Capacitors and all the main Block capacitors.

But I have to say not one of them were faulty when I Tested them on my capacitor Analysers l have 3 different Capacitor Analizers all 3 can put 0 to 600 volts on the capacitor that is being tested.

I have come to the conclusion that I have wasted my hard work and time replacing the Capacltors. They are of such a good quality being in the oil and not drying out If the capitor ls leaking bad that is the only time in the future I will replace one on a AR88. The oil did not affect my hands.

Kevin

[Mans Veldman]

I restuffed my AR-88 capacitors about 5 years ago. I didn't know about PCB's in the oil so I took some precautions. I worked outside and did wear rubber gloves. I put the caps on a metal dish, drilled two small holes in the bottom and collected the oil in a small jar. Then used a blowtorch and pliers to remove the metal bottom. After that I removed the old caps en put them in the jar and washed the empty tins with water and soap.

I disposed of the oil and old caps through the chemical waste collection of our city.

Mans

[Radio Wrangler]

I understand that the nastiest thing about PCB oils is that they create dioxins if they get burned.

I have an AR88 to do sometime, and I know that there is bright red goo that's coming out of the seals. With the insulation of the solder tags in doubt, I don't think there is much point in re-stuffing the bathtub cases, so I think I'll cook up some alternative supports for leaded components. I would have considered opening them with a large soldering iron, but I wouldn't have a flame anywhere near them.

David

[Mark James]

Thanks for all the useful advice - it puts the risks in perspective - I suspected that it had been over stressed. If I need to restuff them I will do it without heat and use nitrile gloves as Latex is rapidly permeable to PCB's.

Mark

[Station X]

Originally Posted by Radio Wrangler

I would have considered opening them with a large soldering iron, but I wouldn't have a flame anywhere near them.

David

You'll never get enough heat in to melt all the solder simultaneously and you'll probably melt the insulation round the tags.

Best method is to drill a hole in the rear cover, then use side cutters to cut and peel it back.

[Radio Wrangler]

The insulation around the tags is already kaput, it's turned to a bright red sticky liquid goo... remember 'Red Hermatite'? I'll have to make something anyway, so I may as well start from scratch.

David

[Aub]

When mine leaked, a few years ago, the colour of it reminded me of red Hermatite gasket compound. I didn't re-stuff mine, but used external capacitors.

Aub

[G6Tanuki]

The "leaking Red Hermetite" is SOP for AR** bathtubs; in the past I've removed them and disposed of them in a sealed bag along with the kitchen-towels used to clean up any remaining 'goo' from the chassis, then used a piece of paxolin and some 'turret tags' to make up little panels on which to mount replacement triplets of capacitors.

Done properly it doesn't look out of place - after all, things like the three big W/W bias resistors are mounted that way...

[Mans Veldman]

I had the same problem with the sticky goo. Just removed everything en used some old model Philips (Mullard) standoffs. I find the result very acceptable.

regards Mans

[Radio Wrangler]

That's a neat job, mans.

The trouble is finding good standoffs. I might use some feedthrough capacitors I have. An extra 1000pF shouldn't cause any problems unless I hit a resonance with the inductance of the film capacitors.

David

[jamesinnewcastl]

Oh er,

Read this a day late since I emptied out a 4uF 'Oil Filled' can yesterday! Naturally this was done without gloves on the kitchen work top. No oil in it, if you define oil as a viscous liquid, mine was basically tar which dissolved nicely in white spirit. In fact the 4uf was 2 x 2uF rolls.

I used a dremmel with a cutting disc to open the back up, no effort and it didn't distort the can. The dremmel also cleans metal parts (even nuts and bolts) a treat with the flappy disc thing. It now ranks with my angle grinder for sheer time saving and joy of use!

I have to empty a tubular can too, which is pretty much tar again.


James

[Station X]

Bath tub capacitors as fitted to the AR88 definitely contained oil. It's possible it's leaked out round the tag seals.

[deliverance]

Very neat good stuff Mans .