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Old 13th Feb 2017, 8:34 pm   #1
PsychMan
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Default AR88 Smoothing Block Ideas

I have an early AR88 receiver and the smoothing block has leaked oil all over the case. The gentleman who sold me it had plugged it straight in to "test" it, and I notice it was also in the trans position, hence why the smoothing block is shot

From what I can see, most people run the original smoothing block with no problems. But now this has overheated and leaked, I expect its beyond salvation, and I dont want to find any nasty oil slicks in the future.

I was looking to drain the can and fit new capacitors inside but I'm finding myself chickening out.

The much debated oil seems to take on a tar like consistency when cool and has proven quite tricky to remove from the case and I can see this being an unpleasant task having to warm the stuff to drain it and then using heat to open the can - all while observing precautions for handling hazardous substances. Some of the bathtubs have leaked oil, but I may just fit stand offs, as other members have done.

The smoothing can does pose another challenge, if I replaced it with something else, the set would not look original the minute the lid was opened, while the bath tubs would be hidden.

Has anyone else replaced the whole block instead of draining and re-stuffing? I'm wondering if I should measure the block and approach a metal fabricator to see if they can copy it. I like the idea of original gear, but if it doesnt work as it did then for me, I cant see the point.
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Old 13th Feb 2017, 8:53 pm   #2
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Default Re: AR88 Smoothing Block Ideas

I found (and there's always the proviso that there may have been detail changes in component construction over the AR88's production span) that the smoothing block assembly has two small rivets holding the retaining plates that secure the actual smoothing block into an outer can. Once the rivets had been knocked out, the assembly could be dunked in a pan of boiling water with the result that after a few minutes, the block slid neatly and cleanly out of the can. It was a bit of simple metalwork to make a new baseplate with terminals to meet the existing loom connections, with attached retaining cradle for 3x 4.7uF 630V ERO polyesters, all hidden under the original outer can. The only give-away is that that the can now rings metallically hollow when tapped, rather than the dull knock of the PIO-crammed original.
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Old 13th Feb 2017, 9:05 pm   #3
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Default Re: AR88 Smoothing Block Ideas

If the oil is the hazardous type, then it's on the loose already.

Opening the capacitor case is going to mangle it somewhat, I expect, so for my AR88 when I get round to doing it, I intend to make a new capacitor case. I'lleither fabricate one from aluminium, or make a composite one uaing 1/16 inch glassfibre from PCB material with the copper etched off Either way, it gets painted and can be made to look original enough.

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Old 13th Feb 2017, 9:10 pm   #4
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Default Re: AR88 Smoothing Block Ideas

I've seen the smoothing-block replaced by a folded U-shaped aluminium section and three of this kind of Sprague can electrolytics sticking out the top.

Seems sensible to me, but there again I'm much more focussed on function and reliability rather than superficial appearance.

"Llisten to it don't look at it" being the radio equivalent of the classic-car philosophy "Don't polish it, drive it ! "
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Old 13th Feb 2017, 10:02 pm   #5
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Default Re: AR88 Smoothing Block Ideas

Bit more time.... Yes, I was prompted to replace the original block by the as-acquired "Exxon Valdez" nature of the AR88 baseplate, too- I wouldn't be too harsh on the seller, both the capacitor block base terminal seals and the solder seams can give way over time and a little oil goes a long way, there being more than a little oil in this case. Normally, I'd go for pragmatic effectiveness in replacement components too, but in this case the easily-resolved can-within-a-can construction meant that the solution outlined above actually turned out to be about the easiest route, in that the existing wiring could be reconnected straight back in place without scrappy jointing, as well as being cosmetically pleasing. The original outer can does have practical use, too, in that the heavy receiver can be inverted for maintenance with rear weight resting on this can and opposite mains transformer shrouding.

The directly-heated 5Y3GT of original fitment results in HT appearing within a second or two of switch-on- whilst the VR150 fires and damps peak voltage rise in "REC", it can still rise well above nominal to start with, so plenty of voltage margin in the replacement capacitors is prudent.
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Old 15th Feb 2017, 11:28 am   #6
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Default Re: AR88 Smoothing Block Ideas

I'm quite intrigued by the boiling method. I'd expect the boiling water would not provide enough heat to burn the oil or produce fumes? Did you find any unpleasant fumes coming off the pan?
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Old 15th Feb 2017, 12:32 pm   #7
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Default Re: AR88 Smoothing Block Ideas

I suppose that the decision had been made for me by the amount of thick and apparently oxidised oil that had crept all over the chassis and the case base- the solder seam at the base of the block had cracked along, possibly electrical leakage had resulted in long-term over-pressure? I was prepared to simply fit some sort of tag-strip arrangement with the new capacitors for functionality, but once removing the block from the chassis had revealed that the actual multi-capacitor was a sealed item (well, originally!) within the outer can, retained in place by the two small plates and a thin layer of wax, I thought I'd try it in boiling water and sure enough, the block was able to slide out of the outer sleeve in short order. Apart from oily/waxy film on the water, I didn't notice any particular fumes or other unpleasantness. As the solder seam was split on the nearly empty of oil inner block, pulling on the terminals resulted in the base easily coming away. This particular multi-block's terminals were hollow Unified screws (with capacitor lead-outs soldered into them) and nuts with shaped 1/4" fitting Bakelite bushes either side and a thin cork sealing washer- far too good to discard!- and were re-installed on the new baseplate in original layout, minus tired and superfluous cork washer of course. I think some other AR88 smoothing blocks have rubber washers and solder tags in the fashion of the bath-tubs, it wouldn't surprise me if thrifting went on as production ramped up.
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Old 15th Feb 2017, 12:49 pm   #8
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Default Re: AR88 Smoothing Block Ideas

As regards presence of PCB oils in these capacitors, I'm sceptical- my understanding is that they first appeared as a lab curiosity towards the end of the 19th century and started to be used in earnest in the 1920s, though they were then very expensive and were reserved for applications where their high boiling point, minimal flammability and reactivity, high specific heat capacity and dielectric strength were most important, such as very large high-voltage transformers that were expected to serve for decades- unnecessary for a low-stress, low voltage application such as the AR88's capacitors where inexpensive and established refined vegetable and mineral oils would have been perfectly adequate. As with many other things, WW2 created a demand for much increased PCB use and that investment in production capacity resulted in them being far more widespread in things like consumer-usage capacitors from the early '50s onwards. All the same, it would be wise to play it safe and minimise handling- one feature of PCBs is their very low water solubility but high solubility in lipids, hence the wisecrack that it's safer to drink them than handle them! Even originally innocuous refined vegetable and mineral oils can oxidise and/or react with other capacitor components to produce unpleasant and originally unforeseen compounds, so the innards of any capacitor should be treated with caution, regardless of quality or vintage.

PCBs really do have excellent properties, hence their widespread usage- it's just unfortunate that they were bad news for life and the environment.
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Old 15th Feb 2017, 8:15 pm   #9
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Default Re: AR88 Smoothing Block Ideas

Quick pic of the retaining plates at each short end of the filter capacitor block that hold the block into its outer sleeve with its mounting lugs, the rivet mentioned using the small middle hole. If these are present, the block is double-skinned and a cosmetic rebuild becomes fairly easy as previously outlined but I fear that some (many?/later?) AR88s may use single-skinned, rivet-terminal filter blocks whose rebuild would be much messier, more unpleasant and more time-consuming than the double-skin, stud-terminal type. I'll post a pic of the rebuilt inner when I get access, but it might take a few courses of Shredded Wheat and Irn Bru....

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Old 16th Feb 2017, 7:31 am   #10
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Default Re: AR88 Smoothing Block Ideas

Thanks Colin, I appreciate that.
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Old 19th Feb 2017, 9:41 am   #11
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Default Re: AR88 Smoothing Block Ideas

I have removed the "guts" from capacitors and transformer cans that were tar filled.
The easiest way I found, is to put a hot plate OUTSIDE and put an old pan of water on it. Then put the item in another can,in the water; making sort of a double boiler arrangement.
So far... it has worked well. the tar can really stink up the shop and if the oil or tar manages to catch fire, having it outside is a good idea. Breathing the fumes can make you quite ill. (Not to mention the XYL might have a "few choice words" with you for stinking up the house with hot tar smell. Fido might have company for the night. LOL)
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Old 20th Feb 2017, 10:02 am   #12
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Default Re: AR88 Smoothing Block Ideas

I had a go last night with boiling water poured into a sink but no joy. I also slid a knife in between the two cans, the waxy potting compound is indeed tough to get through. In the end I gave up as I was bending the can slightly - ill have to knock it back to shape when I complete the job.

I guess I just need the intense heat of a boiling pan as others have suggested , I will source a pan I can do this with outside on a camping stove
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Old 20th Feb 2017, 11:09 am   #13
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Default Re: AR88 Smoothing Block Ideas

I'm trying to remember the exact sequence of events- it's probable that as I found it was easy to pull the base with its failed solder seam away from the can, I tipped the innards out anyway before the boiling-up (I do remember thinking that the capacitor elements were like three dark green and oily squashed toilet rolls, or even large stuffed vine leaves....) so that the empty cans would have much less heat capacity and they separated quite nicely without too much stress. With a complete, full inner block, there's probably a lot more thermal inertia, so it might be worth dropping into boiling water, switching off and leaving for 15 minutes, then turning the wick up again if the wax hasn't softened up sufficiently. I did use a plain old deep saucepan that had been retired from its food preparation days!

I had dropped the capacitor chunks and their residual oil into a chunky jam jar, intending to get them analysed at some point but my partner said, there was some horrible oily old junk of yours in the shed, so I threw it out. Hopefully it wasn't PCB....
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Old 21st Feb 2017, 9:54 am   #14
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Default Re: AR88 Smoothing Block Ideas

Sure, the waste is a tough one. I contacted several waste disposal companies and received no response, probably because they want big contracts and don't care about little me and my small quantities of pseudo-PCB waste.

I emailed my council, who in turn sent my email around various different departments and offices, and in the end they came back to me and said no they don't have any facility to dispose of them, and referred me to another commercial body who did not reply to me!

So unless I can find someone who can sneak it in to a waste bin, I'm basically faced with binning them, or sticking them in jars and retaining them for the foreseeable!
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Old 21st Feb 2017, 10:38 am   #15
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Default Re: AR88 Smoothing Block Ideas

Be careful about contacting local authorities about disposal of potential hazardous waste. They may decide that it's dangerous enough to require collection and disposal of by a specialist contractor, which could cost you an awful lot of money. The onus will be on you to find a contractor.

The only waste I've ever disposed of using a contractor was asbestos. Everything else, which can't be reused, goes in the bin or down the drain.
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Old 21st Feb 2017, 12:21 pm   #16
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Default Re: AR88 Smoothing Block Ideas

That's the trouble with having a conscience! A great many will either be unaware or not care about disposal and simply sling things in the general waste. A long time back, I was helping to clear redundant components from works stores, which included some large tumbler switches with a jam-jar size container half-filled with mercury- I intercepted them as they were about to be flung into the skip with the comment that they really ought to be disposed of properly, my supervisor relented but the resultant paper-trail and expense didn't do me any favours....

As regards stuff at home, I salve my conscience by putting my dubious vintage waste into the general WEEE skip at the local tip on the grounds that even domestic disposal could constitute substantial amounts of mercury, cadmium, PCBs etc. and that it's up to the council to use responsible accredited contractors. I know that's buckpassing, but it's very difficult to check disposal trails with a chain of contractors, commercial confidentiality and so on. Moreover, recycling percentage is "political" and the goal-posts and definitions get stretched so that "recycling" could mean loading into an incinerator for making electricity or cement, or loaded onto the cheapest bulk carrier and dumped onto a faraway beach to be picked over by impoverished people. Ho hum- in an ideal world....

I used what must have been rather expensive aluminium-cased and epoxy-sealed capacitors rescued in that stores clearout, but if I was doing the job again I reckon I would use some of the inexpensive and widely available polypropylene motor-run capacitors of typically 450VAC rating-these ought to be fine to 600VDC and there are lots of suppliers of 4, 4.5 and 5uF types that would easily be accommodated in the original block footprint- I believe its voltage rating was 550VDC. A pragmatist would say that modern 500V electrolytics would probably be fine but somehow that wouldn't seem in keeping! In the next couple of days, I hope to make space and time to get at the set and kill two birds with one stone by trying the reduced heater volts mod to the 6H6 noise limiter, which is supposed to reduce susceptibility to hum.
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Old 22nd Feb 2017, 10:47 am   #17
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Default Re: AR88 Smoothing Block Ideas

I agree with the comments with regards having a conscience, not easy these days!

I had attempt number 2 last night, and submerged the unit into boiling water for around 20 minutes. At various points I tried to separate the middle can using large grips to hold the can and pliers on the capacitor terminals, no movement at all.

A lot of nasty potting compound did come out however and it was a messy task. I may have another go as I suspect more time boiling will eventually remove all of the wax. I don't relish the task and the cleanup though. I did measure the can as best I could and am waiting on a neighbour to provide a quote on fabricating a replacement, which may prove the best option.

I'll try and get some pictures up of what Im doing, it may help somebody see how NOT to do it

One observation however, the aerosol version of jizer available in Halfords did do a fantastic job of removing the gunk from my tools afterwards, along with a small tooth brush to agitate.
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Old 24th Feb 2017, 12:40 am   #18
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Default Re: AR88 Smoothing Block Ideas

Sorry to hear that removing the outer shell has been something of a PIA... maybe the capacitor block in mine had less or softer waxy stuff holding it in, or maybe it had deteriorated so that it let go more easily. In a way, I'm surprised that the various sites that discuss the AR88 don't mention something along the lines of what I had done to substitute for the original C96, 97, 98 trio, seeing as it seemed to be a straightforward and effective solution that retained the original shell, as the construction means that the messy disembowelling usually necessary with restuffing ols outer cases isn't necessary.

A couple of piccys to illustrate what I did- the capacitors were Evo-stikked to a piece of angle steel which was fixed to a base-plate drilled to suit the original chassis holes and fitted with the salvaged terminals in the original layout, stood away from these terminals with 4x 4BA threaded pillars, screws and nuts. Simple,quick to make and quite crude in retrospect. The original hollow terminal screwheads can just be made out by the hex pillars, the shouldered insulating bush concealed under their relatively broad heads. I wanted to keep the outer can, as it's an important safety feature here- one of many good points about the AR88 is that it's notably safe with the case lid open- unlike the slightly terrifying BRT400, for example!- a feature worth maintaining. Each to their own, but I find a bit of adapter plate/bracketry making quite satisfying if it avoids having to drill/otherwise scar the original metalwork- after all, it was a rather nice and expensive radio in its day and deserves a bit of effort. Perhaps I've seen too many nice bits of kit with toe-curlingly bodged, even dangerous work done on them....
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Old 24th Feb 2017, 10:08 am   #19
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Default Re: AR88 Smoothing Block Ideas

That's a very neat job there!

I've asked my neighbour if he can quote for a plate to go underneath the replica can. The screws for the can would go through this also in a similar way it did with the original clips that hold the inner can. I can then drill the plate, add insulated terminals, and mount some polyester capacitors on the plate so its all inside the can. I will also look for some spray paint so the can is as close to the original as is possible.

If the quote comes back low enough I think I will take this option.
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