Ekco U353 Restoration

[lesparapluies]

Having wrestled the Westminster radiogram into submission I thought I'd tackle a table radio next, to help fill the long dark summer evenings ahead(!) - picked up an Ekco U353, cabinet in lovely condition. I resisted the temptation to plug it in, even through a dim bulb, and, after inspecting its interior, this was probably a good thing. There are several issues, but I think the first ones concern the power supply. The supressor capacitor across the mains switch (C60) has literally fallen in half (see photo) - I will replace this with a type X capacitor unless anyone advises otherwise. The main smoothing / filter caps (C57, C58, C52) are all in the same can, and the terminals have corroded so badly that they too have fallen apart. I think I'm just going to remove the can altogether and replace these with new ones mounted on a tag strip, rather than trying to preserve the appearance. C57 and C58 are obsolete values (40uF) and I think it will be OK to put in 47uF ones rather than going down to 32uF - I've seen lots of similar circuits with UY85 rectifier which use 47uF so presume it will tolerate them. But one thing which concerns me is that there is a capacitor soldered across the existing C52 - not in the circuit diagram and almost certainly added later, as it's an RS component, which none of the others are. C52 is 32uF and the "new" one across it is 16uF - any ideas as to why that would have been fitted? Thank you in advance for any input.

[ajgriff]

Coincidentally I'm working on a U353 and the wooden cased version (U362) at the moment. So far I've removed the C57/58/52 can (original I think) from the U362 and C57 & C58 are both actually marked as 50uF so I'm sure 47uF will be fine. It looks like the RS capacitor was someone's idea of a quick fix to try and bolster a failing 32uF C52. Won't be needed when the new capacitors are fitted.

Alan

[lesparapluies]

Thanks for that Alan, will be interesting to compare notes..

[PJL]

Don't touch the dial glass as these are renown for the markings falling off with the lightest of touches.

[lesparapluies]

Yes, thanks, I'd already read about that! My wife has done wonders with the plastic cabinet but was warned to "Keep Off The Glass"

[lesparapluies]

Update - have done a bit of cleaning up and removing components which obviously need replacing. Now then, capacitors... I'm going to replace all of the electrolytics and the two large waxy ones (the supressor across the switch and the similar one from the chassis to the earth socket, as a matter of course. But regarding the others - several are ceramic discs which I understand are normally OK so I think I'll check they aren't wildly out of value and leave them be. There are some square items which have a hard surface finish and I'm assuming these are ceramics, but there are some which look a little similar but are oblong and waxy - am I right to think these are paper / wax, and probably bad? Also, there is one capacitor which comes off the centre pin of the volume pot, and which seems to be a screened capacitor, i.e. it has the normal 2 leads plus a 3rd which is connected to chassis. In my 50 years or so of tinkering with electronics I've never seen one before, nor can I find any reference to them on the internet...any comments? Many thanks, MD

[paulsherwin]

Anything smaller than 0.001uF is likely to be OK. The TCC aluminium cased caps in the first two pics are likely to be bad, as is the Hunts Mouldseal in the second pic.

[ajgriff]

Unlike Paul I can't actualy spot a Hunts Mouldseal in the photos but there are a number of them hiding away in my U362 version of this chassis and they're all on the list for replacement. Some of them are quite badly cracked.

Out of interest I think that it'll be possble to reform the x3 electrolytic can in mine but won't know for sure until I try it. A couple of higher wattage resistors in the same part of the circuit have risen substantially in value and will be replaced.

Alan

[paulsherwin]

The Mouldseal is the component with the white sleeve in the first pic (not second, sorry) with '400V' visible on it. Lots of Mouldseals in Ekco radios are sleeved like that, I've no idea why.

[ajgriff]

Thanks Paul, I see it now. I was hunting in the the wrong photo!

Alan

[lesparapluies]

Thanks for replies, I see the white Mouldseal one. The two high power resistors have also gone high in mine Alan, the 820R almost 1K3 and the 330R about 390R..no chance in reforming the power capacitors, the terminals have all corroded away and broken off, worst I have ever seen, yet other parts of the layout are OK. Any comments on the shielded capacitor? If it needs replacing I'll just use a normal one and put some grounded foil round it if necessary

[dazzlevision]

Originally Posted by lesparapluies

Also, there is one capacitor which comes off the centre pin of the volume pot, and which seems to be a screened capacitor, i.e. it has the normal 2 leads plus a 3rd which is connected to chassis. In my 50 years or so of tinkering with electronics I've never seen one before, nor can I find any reference to them on the internet...any comments? Many thanks, MD

The metal case of this capacitor is screened (and connected to chassis) in order to reduce hum pickup, which is a common problem on ac/dc sets, particularly in this high impedance part of the audio circuit, with low levels of audio signals.

The square beige colour capacitors are ceramic dielectric and unlikely to be faulty.

The oblong wax dipped ones will be silvered mica dielectric and unlikely to be faulty.

[paulsherwin]

It looks as if the cap you mention just has a chassis connection clipped to the aluminium case to minimise hum.

It should be OK if you just replace it with a conventional plastic film cap.

[lesparapluies]

Update - In the course of the restoration work I noticed that one side of the mains switch wasn't working, so instead of sitting down and working out a safe way round this (e.g. by using a simple relay), I immediately removed the whole dual pot / mains switch unit and recklessly dismantled it. Fortunately everything went back together OK, I cleaned the pot tracks and got the switch working, but I'm faced with a slight problem - the switch was secured to the rear pot case with some soft metal rivets, which came adrift quite easily and can't be put back. I think I can probably re-secure everything with two thin self-tappers (see pictures) but as a "belt-and-braces" approach I'd also like to glue the switch assembly to the back of the pot - question - which glue would work best? I'm thinking of something like Evo-Stik, an impact adhesive, but I've noticed a few references to epoxy glue in other postings , any suggestions? Obviously it's metal to plastic

[ajgriff]

Strangely enough I had a similar problem with the chassis of the wooden cased version although it was caused by my own carelessness. Basically I was desoldering the remains of the 0.01uF cap (C60) fitted across the incoming mains with the chassis standing on its end. The chassis toppled and landed with due force on the spindle of the dual gang switched pot. The result can be seen in the first photo. The pressed mating arrangement could no longer be persuaded to do its job. From past experience I didn't think that impact adhesive would have sufficient strength for this repair so I used two part epoxy which seems to be holding firm but only time will tell. If it doesn't hold I'll use Unibond Repair Extreme which I'm sure will work but I didn't want to open a new tube just for this as it doesn't stay usable for very long once opened.

In case anyone is tempted to mention it, I know I should have got around to constructing that long promised chassis stand!

Alan

[Station X]

Originally Posted by lesparapluies

Update - In the course of the restoration work I noticed that one side of the mains switch wasn't working, so instead of sitting down and working out a safe way round this (e.g. by using a simple relay), I immediately removed the whole dual pot / mains switch unit and recklessly dismantled it. Fortunately everything went back together OK, I cleaned the pot tracks and got the switch working, but I'm faced with a slight problem - the switch was secured to the rear pot case with some soft metal rivets, which came adrift quite easily and can't be put back. I think I can probably re-secure everything with two thin self-tappers (see pictures) but as a "belt-and-braces" approach I'd also like to glue the switch assembly to the back of the pot - question - which glue would work best? I'm thinking of something like Evo-Stik, an impact adhesive, but I've noticed a few references to epoxy glue in other postings , any suggestions? Obviously it's metal to plastic

Judging by the rust that looks like a steel case. Could you soft solder couple of nuts to it?

[paulsherwin]

When I need to drill out the rivets to dismantle a pot I replace them with small nuts and bolts. No need for glue in addition. If you glue it with epoxy you won't be able to dismantle it again if necessary.

[ajgriff]

I agree that small nuts & bolts would be the ideal way forward although I think it will involve further dismantling. No rivets involved in my accident and gluing seemed the best option. Judgement call as always.

Alan

[lesparapluies]

Thanks for replies. I had also thought the nut and bolt option was the best one to take but the problem is that, although the front pot came apart very easily after bending the lugs back, the rear pot refuses to be dismantled so I can't get to the back of the 2 holes to secure a nut. I have tried every method of gentle persuasion but unless there's something I'm missing, the shaft and track assembly will not be parted from the outer casing

[lesparapluies]

Alan - two-part epoxy is something like Araldite, right?