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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 18th Jul 2008, 10:55 pm   #1
Zelandeth
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Default Marconiphone T19A

Figures, don't it. The first set that I tackle on behalf of a friend rather than for myself, and it decides to put up far more of a fight than any set I've actually owned so far!

Obviously as this was being tackled for someone else (albeit for someone with decent electrical knowledge themselves), safety was paramount, so questions were asked here at any step where I was even vaguely unsure about.

Unfortunately, I don't have any photos of the set as recieved as muggins here missed a folder when backing stuff up prior to reformatting the harddrive - that's another story though! It looked to be in pretty good order though - both inside and out. The case really needing nothing more than a good polish up to get it looking like new - even the back was immaculate. Upon removing the back panel, everything was covered in an even layer of dust, no sign of anything having been disturbed recently. Taking the bottom cover off revealed a shedload of oozing wax capacitors, flakey carbon resistors, and a leaky mains smoothing can which looked to be evolving into an entirely new lifeform. Lovely!

Paul Stenning's Site as usual provided me with all the service data I needed in seconds - so armed with that, a couple of screwdrivers, and my very beat up looking soldering iron, time to get cracking.

First step of course was to replace the (obviously) knackered smoothers, and the grid coupling capacitors for the output valve - in this case a DN143 (EBL21). It became apparent at this point that one of the smoothing caps had been replaced at some point in the quite distant past already - irrespective of that, I replaced both of the discreet ones. Two further electrolytics exist in a can above the chassis in this set - these however measured okay, so I decided to see if they'd play ball - somewhat to my surprise, they did.

At this point, the set was powered up on the lamp-limiter to see if I could coax any signs of life from it - unfortunately very little was my reward aside from a couple of crackles. Somewhat disgruntled, I set about replacing the rest of the disintegrating capacitors. All waxies were replaced with the yellow 1kV rated polypropelene types from RS which I'm a great fan of due to their similar size to the waxies, and the fact that they come with long, flexible leads which seem to be nigh on impossible to snap. By this point I realised something: The tag-strip based design Marconi had decided on for this set minimised the amount of spaghetti under the chassis quite a bit, and makes a circuit diagram quite easy to follow - however it's an absolute pain to work on unless you've got twenty-five quadruple jointed fingers as thin as cocktail-sticks and a soldering iron to match. I don't think I've managed to burn my fingers quite as many times when working on any set as I did on this. A quick check of the somewhat tired looking carbon resistors that were flaking paint all over the place revealed that they were all between 20 and 40% high, every single one of them...out came the soldering iron again...

Thanks to the fairly easy to follow - if awkward - layout, I didn't go to the lengths of testing the set after replacment of each component in this case - especially as I didn't really have any test-result to start with!

As you can imagine - I was somewhat irked when first switch on following this work was resulted with glorious silence aside from a soft hum from the mains transformer. Hmm...out with the multimeter to make sure that I've not done something really dumb - and the first plea for help appearing here. Some excellent detective work by you folks out there quickly tracked this down to a low-emission DN143. This was evidenced by the valve only drawing around 20mA of anode current when the bias conditions should have been resulting in nearer 80mA. This was evidenced as well by the fact that I discovered that there WAS actually audio...just very, very, very quiet audio. A quick call to Valve & Tube Supplies (no association other than as a happy customer) resulted in the fastest response I think I've ever had to an email, and a new valve appearing on my doorstep very shortly afterward.

The new valve got it up and running - accompanied by the spectacle of me throwing myself backwards across the room in shock at the sheer volume of noise produced by the set when it burst into life (I'd not turned the volume down!), as it happened to be perfectly tuned into Radio Scotland!

While this had restored the set to life, all was not well yet however, there was still a very pronounced hum, the tone-control only worked when it felt like it, and reception seemed really rather poor. First port of call I decided for the hum was the remaining couple of electrolytics. Replacements were ordered, as they weren't values I had in stock...which seemed impossible given the amount of caps I stocked up on earlier in the month!

At this point, a break for the best part of a month took place, as I had friends up visiting from London, and there was barely enough space to move in the flat with an extra three people here, never mind work on a radio - not that I had time anyway. The case was returned the set's owner at this point to be taken to a gentleman he knows specialising in furniture restoration to be polished while I was on holiday.

Fitting the replacement electrolytics cured the hum problem instantly, and seemed to have improved reception greatly - though I'm not entirely certain if that were the case, or it was just that I had the set in a different place when working on it that time! These were secured near to the original can under the chassis, which I left in place for aesthetic effects, and because it provided a ground point for other components which I would have had to recreate if it was removed. I did consider re-stuffing the can, but on this occasion decided that as time was an issue, and that the owner was more concerned with the set working as well as it could without too much concern over what it looked like below decks, to just secure the new caps properly and not worry about it. One was anchored to the original can itself, the other slotted nicely in beside the frame of the output transformer (after I checked that this didn't cause any hum of course). I also dismantled the tone control pot at this point and discovered that it was full of dried up grease - a good clean up restored smooth, consistent operation.

By this point, the case had been returned to me. I gave the back of the tuning scale - a strange material this...kind of like a cross between velvet and a fuzzy-felt backing board in a brown colour - a good clean, and carefully cleaned the tuning scale itself. Thankfully the print on this one was very solid, so this wasn't too hard. The same proceedure was carried out for the speaker baffle, before I reassembled everything. Getting the tuning cord back into its groove is a royal pain I discovered, but just requires patience - if you prod it in the right direction enough times, it eventually lands where you want it to! The chassis was then resecured to the case.

The owner had requested that the mains voltage adjustment panel be left visible on the back - but need not be operational - so the voltage selection was set to the highest range directly and the selector itself disconnected, with the ends of the wires suitably sheathed and secured.

A new three-core mains lead was then fitted and secured, with the chassis earthed. The 13A fuse found in the plug had already been replaced with a 3A one by this point.

The dial-lamps were *finally* replaced at this stage (for some reason, Maplin took forever to get them in stock - I was about to bite the bullet and pay five times their worth in P&P to order them online), which made the set look a lot more presentable, as they'd both been different types before, one being far brighter than the other.

The set by this point seemed to be performing well - even just with its built in antenna (the speaker grill - interesting idea). So, it was set up on the corner of my desk, and left running for a soak-test. Given the number of parts replaced, I decided I wanted a good few hours on the set before I called it done - so it was left to run all evening when I got in from work until bed for the best part of a week. It performed faultlessly, though one observation is that the back panel does get quite toasty next to the DN143 - not alarmingly so, but enough so that if you've got one with a duff back and are making a new one, it might be worth adding some extra vents in that area.

All in all though, a success - even though it had a somewhat offputting beginning with the no-audio fault appearing. It's not a hard set to work on, you don't need to shift miles of wire or dozens of other components to get to anything - though the tag-strip is awkward to work on. The only other gripe is the lack of a detachable speaker - this makes the chassis itself very cumbersome to handle when it's out of the cabinet - adding a couple of discreet connectors to allow this to be removed would probably be worthwhile - I'd run out of them however, and forgot to order any with the re-stock done at the start of the project.

Despite the fact that this ran over the course of the best part of three months - I didn't have a single screw or washer disappear, nor did I end up looking at anything at the end thinking 'where did this come from' Basically because copious notes were taken at each state, and everything was put into little ziploc bags which I then labelled things like "Back panel" "chassis mountings" and "Scale fixings." Obsessive? Maybe - but it obviously works! I should point out that the service-data printouts now look rather more like one of Da Vinchi's designs now than the original data with the amount of scribbles on them - that's what they're there for folks!

All in all, an enjoyable if at times somewhat baffling restoration this one. Lovely sounding set too.

...Fingers crossed, it won't be back with another fault next week!

Next up: Bush AC11 I think!
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Old 18th Jul 2008, 11:29 pm   #2
matthewhouse
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Default Re: Marconiphone T19A

Very interesting restoration, I do very much like this range of Marconi radios.
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Old 18th Jul 2008, 11:40 pm   #3
Steve_P
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Default Re: Marconiphone T19A

Glad it's sorted old boy! Nice set. Marconiphone stuff generally is.

Cheers,

Steve P.
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Old 19th Jul 2008, 12:30 am   #4
Zelandeth
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Default Re: Marconiphone T19A

Knew I had a picture of the innards somewhere too. This was shortly prior to completion, where I still had to remove a bit of dust, fit the new mains cable and to tidy the wiring up a bit.

Not exactly the best angle either, but gives you an idea of the layout. The small heat shield next to the DN143 actually does a surprisingly good job of deflecting the heat from it away from the mains transformer.

I did find the choice of the U143 as the rectifier a bit of an oddball compared to the other valves though - not that I'm complaining - it was the only one I wasn't convinced I was going to break when taking them out to clean them - this certainly isn't a set where you need to worry about the valves falling out in transit. ...or even if the set is dropped from a 14th floor window. The valveholders have a VERY good grip on the valves!

I have to admit that the whole set has a really well made feel to it, even without the chassis in the cabinet weighs a ton!

The one thing I forgot to say in the original post of course - was a very big thank you to everyone here who helped me out with it when I got stuck!
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