Ekco U332

[geofy]

Originally Posted by oldticktock

If you go for the RT&S one that's available, on page two is the full schematic i'm looking at it as we type now ( my book). Pauls link is just showing page one as a teaser

Chris

Thanks Chris though I don't have the RT&S, I expect I can find my way round without the schematic, just makes things easier.

[wd40addict]

My girlfriend (now wife gave me one of these a couple of birthdays ago. It's suprisingly sensitive and sounds good. However I had to change a couple of the valves as both the UCL82 and the UBF89 seemed to have developed internal leakage causing audible distortion and poor AGC. Changed the odd cap and resistor as required. Quite unusual this as I've rarely had to change any valves in sets I've acquired. Anothe bizarre fault was that back in the day half the on/off switch had been bypassed (rather bad for AC/DC safety) and now the remaining section was duff. A rebuild of the pot and switch fixed this.

Regards,

Paul

[geofy]

Originally Posted by wd40addict

My girlfriend (now wife gave me one of these a couple of birthdays ago. Anothe bizarre fault was that back in the day half the on/off switch had been bypassed (rather bad for AC/DC safety) and now the remaining section was duff. A rebuild of the pot and switch fixed this.

Regards,

Paul

Hi Paul, These seem to be a popular set, the UCL82 has a 50 Volt heater so maybe that is why they have a bit of a hard time. But valves do last a long time as a rule, I have only had one valve failure in my Philips, an EBL1 after 'only' seventy years of use (not by me)! The switch in my one is ok at the moment. By coincidence I never turn off the somewhat delicate switch in my Philips 650a, just unplug it each time.

[wd40addict]

Even though I've fixed the switch I tend to just turn it on and off at the mains and leave the volume set where I want it. Better safe than sorry.

Regards,

Paul

[Tony1951]

Originally Posted by geofy

I have only had one valve failure in my Philips, an EBL1 after 'only' seventy years of use (not by me)!

Excuse the greenhorn question, but how long do valves usually last? I ought to know this having been brought up with valve radios and TVs as a kid in the 1950s, but I can't recall too many problems of blown valves. Obviously there are different sorts - the directly heated battery cathode valves are expected to have a short life, and some sets may be ill-used, but with mainstream valves, how many hours of use is typical for say an output valve and in contrast, let's say a front end mixer oscillator?

[geofy]

Excuse the greenhorn question, but how long do valves usually last? how many hours of use is typical for say an output valve and in contrast, let's say a front end mixer oscillator? [/QUOTE]

I was also brought up on valve TV, a DER Thorn, probably 950, which was on every evening, and seldom needed any attention until DER started to fall apart as a company and we where given dodgy replacements when it did need attention. And a Regentone radiogram which only broke down after many years, and that was resistor failing and not a valve. Small valves will last a long time, especially the RF ones, some might fade rather than go altogether. My Philips still has its original valves apart from the EBL1 which developed a heater-cathode short, seventy year old and still working, and my Dynatron Mimco is nearly sixty with its original valves. But to keep on topic this Ekco dates from the late fifties still with its original valves though it hasn't been switched on for a long time.

['LIVEWIRE?']

Last year I overhauled two Ferranti U1015s(same set as the EKCO) They are quite easy to work on. As I usually do with sets of this vintage, I changed the reservoir/smoothing Capacitor, all the 'orrible 'unts!', and any out-of tolerance resistors, plus, in one case, the on/off switch/volume control. Both worked very well after the repair.

[geofy]

They look an easy enough set to work on, couldn't get a much simpler power supply. I am hoping the 50uF electrolytics will still be ok, the radio works well with all its original parts, didn't even object to being switched on after years of not being used. But I will be checking them as the inside needs a clean. I don't intend using the radio for long periods anyway.

The extension speaker is just across the isolated secondary with one side going to mains earth, so it could put a strain on the O/P transformer insulation if connected to earth. There is also a feedback winding on the secondary.

[geofy]

Opened up the set, extracted a long dead spider and web, just what do they find in there. Can see where the Alien film got its idea from. There are four Hunts 0.01uF waxies of different sizes that will need changing, a couple of 0.03uF. The 0.05uF mains filter can be replaced with an encapsulated mains filter that I have. The low value Lemco capacitors are also waxed covered but these won't need any attention. The dropper has a few cracks in the green coating.

[geofy]

A progress report as I am in no hurry to get this set back together, so can spend time on the trivial things. I used a drop of Plusgas dismantling fluid on the two front control knobs and the side waveband switch knob, and left it for an hour, I still had to use a vice (mole) grip on the handle of the small screwdriver while pushing it down to turn the screws in the front control knobs. The two screws holding the main chassis where treated with the same, these held two brackets slotted into the case. The loudspeaker had two slightly rusted screwthreads and two clean ones, these must have been assembled with rust on them from new, all four where very tight and took a few attempts to move them. The chassis and speaker where withdrawn.

I cleaned the inside of the cabinet with a dry paint brush to get rid of the dust (outside the house!), then a damp cloth to wipe the remaining dust away, with some soapy water, making sure I kept away from the dial to avoid messing up the markings. The dial plate and speaker front where never intended to come out again as they have the 'fit once' spring clips which would break if touched, so I left them alone. The clips are a bit rusty so will need treating.

The speaker was unsoldered with my 25 Watt Henley Solon, it made me wonder if the joints had been made with the same type of iron. The speaker frame had some light rusting which I treated with Hammerite rust remover, applied with a blunt screwdriver, after wiping off there where small patches of bare metal, I have some Humblol paints and the grey enamel number 106 was a near match so this was dabbed on with the same screwdriver and left to dry. The Elac badge also needs glueing back on.

Next the chassis will need cleaning and the components checked. THAT cap or more correctly two of them, the grid from the volume control and the output valve grid are both TCC metal types and probably can be left as these are better than the Hunts waxies, of which there are only two of those. I will be taking the cream waveband knob to the DIY shop to try to get colour match, it might get a few odd looks as I hold it against the paint tins so I will have to wear my best anorak.

I take a few marco pictures of the chassis as this can help in planning the work needed, as the pictures can then be viewed at leisure on the screen without having to handle the chassis each time until the actual work needs doing.

[geofy]

If I could ask some advice on resistors, in the diagram the main one I am concerned about is R2 the AGC resistor which measures 1.3M, the only combination I have are two 1.6M metal oxides to make 800K, it gets unwieldy if I also put a 100K in series to make 900K, is 800K suitable in this position as it would increase the AGC feedback or better just to leave it until I can get a 1M.

R1 10K has risen to 12K, and R3 47K, and R4 4.7K, have gone up curiously to around 62K and 6.2K receptively. And yet the 4.7M still measures correct. The 22K and 2.2 K have also gone high and have already been changed. The 470K across the IF still needs measuring by disconnecting.

The 0.01uF safety capacitor from chassis to mains earth was just an ordinary Hunts waxie. I will probably leave the larger 0.05uF Hunts mains spike bomb in place just for show after disconnecting it. All the Hunts actually still measured ok, even though the safety one was pressed against the HT 3.3K 2Watt HT resistor, melting the wax!

[Steve_P]

R1 will probably be OK.
R2 might be OK at 800k or 900k, but 1M is easy to obtain and will be easier to fit.
R3 and R4 are easy values to obtain if you want to change them.

Just change any Hunts caps that have HT on them, are safety parts or have melted.

Cheers,

Steve P.

[geofy]

Originally Posted by Steve_P

R1 will probably be OK.
R2 might be OK at 800k or 900k, but 1M is easy to obtain and will be easier to fit.
R3 and R4 are easy values to obtain if you want to change them.

Just change any Hunts caps that have HT on them, are safety parts or have melted.

Cheers,

Steve P.

Thanks Steve, I already have the values for R3 and R4 so they are next to be changed, along with the 22K and 2.2K

When I bought replacements from Savoy Hill they only had values up to 56K and other places don't seem to sell single resistors. I will try Maplin.

The Hunts are being changed. I am leaving the TCC types, one is the main double smoother can which still mesures spot on.

[geofy]

I don’t have the factory voltages for this set and have measured the actual voltages and put them on the diagram. To work out a value for a capacitive dropper I am assuming 10mA for the UCL82 to give a maximum output of around 1.6W though normal listening will only be a quarter of that at most. And measured approx. 18mA across the 3K3 for the rest of the HT circuit and 100mA for the heater chain after it has warmed up. A total of 128mA and an AC to the rectifier of 172V. Does this sound about right as I have never done this type of modification before. A transformer with a 172 secondary would be better but I don’t expect there is such a thing. I wonder if such a transformer could be made, 200mA would not make it very large, an auto-transformer might work if it had a suitable tapping.

If I could ask some advice, the grid of the UCL82 measures +4.6V and the cathode +8.7V making the grid – 4.1V wrt cathode. Does this sound reasonable?

[Steve_P]

I am sure you have changed that capacitor.

There shouldn't be 4.1v there, try another valve. The UCL series tend to go funny at the drop of a hat.

As far as Capacitive Droppers go, I wouldn't bother until the rest of the set is sorted. Then go here:

http://www.vintage-radio.com/repair-...per-calcs.html

Cheers,

Steve P.

[geofy]

Originally Posted by Steve_P

I am sure you have changed that capacitor.

There shouldn't be 4.1v there, try another valve. The UCL series tend to go funny at the drop of a hat.

Cheers,

Steve P.

Thanks Steve, the 4.1V is minus with respect to the cathode, the radio works fine and there is no overheating of the valve. I don't have any spare valves. That cap is still original, but it is a TCC metal tube type and still gives correct capacitance, I know there can be a problem with ESR but surely the radio would not work as well as it does if the cap was faulty.

I would still like to get rid of the 100 C dropper.

[geofy]

After buying a 240/120 voltage adapter I extracted the transformer, which was a fully isolating type. The wall wart had those screws with a raised middle ridge but come undone easily with small long nose pliers end on. (What to do with the empty plastic box). A test run with a 15Watt fridge bulb showed the secondary give bang on 120VAC and after half an hour the temp of the core had risen to 32C which was acceptable. The transformer is rated at 45 Watts but in a plastic box with hardly any ventilation due to CE rules blocking most of the small vent slots I should imagine the transformer would get very warm at max rating.

I decided to play safe and keep the 430 Ohm heater dropper section in place and put 120VAC straight on the anode of the UY85 rectifier. The sets mains plug tucked out of the way as the top end of the dropper was still connected so would have volts on it. A temporary lash up was made and the bypass mains plug to the transformer plugged in. The heaters took longer to warm up but when they did the radio worked just as well as when it had higher HT, some slight distortion if the volume was turned high but plenty of volume at lower setting. The heater chain calculates at just under 80 Volts. For the amount of use the radio will have I am tempted to leave it like this and find a way to fit the transformer which doesn't have any fixing points.

The sound clip, if you can play it, was taken at less than quarter volume tuned to Absolute radio 247m. Earlier Pink Floyd's "Brick in the Wall" was played and it gave a very satisfying bass note. Though it is questionable as to whether they don't need no education (double negative!). How does a fifty plus year old 7 by 4 speaker sound so good. After an hour the transformer temp reached 35C (sitting on cardboard) which is better than the 100C plus of the dropper. Mains hum is virtually non existant even with a sliglty leaky UCL82.

[Jamie-Skinner]

Originally Posted by Boom

That's very interesting. I've never seen an ac/dc set with an extention loudspeaker socket.

My U353 has the extension loudspeaker socket and is also an AC/DC?

Mind you.. Most EKCO's had this.

[PJL]

Originally Posted by geofy

Thanks Steve, the 4.1V is minus with respect to the cathode, the radio works fine and there is no overheating of the valve. I don't have any spare valves. That cap is still original, but it is a TCC metal tube type and still gives correct capacitance, I know there can be a problem with ESR but surely the radio would not work as well as it does if the cap was faulty.

ESR is not important here as it ia part of a very high impedance circuit. You are interested in leakage current at the working voltage. TCC capacitors are not much better than wax coated capacitors for leakage. You need to replace that capacitor.

As you can see from this http://www.mif.pg.gda.pl/homepages/f...10/u/UCL82.pdf the normal operation of a UCL82 is with -11.5V. (it will be a bit less than this as the screen is only 100V)

[geofy]

Originally Posted by Jamie-Skinner

My U353 has the extension loudspeaker socket and is also an AC/DC?

One side of the speaker and the speaker chassis is connected to safety earth this goes to one side of the extension and signal earth socket. The safety earth is connected via a 0.01uF capacitor to the live chassis. This should be X2 rated but the original is an ordinary Hunts.

I have fitted an AC only transformer and bypassed the dropper to make it AC only, though I may have to supply the HT with a resistor from the AC mains with only the heaters being supplied from the transformer.

ESR is not important here as it is part of a very high impedance circuit. You are interested in leakage current at the working voltage. TCC capacitors are not much better than wax coated capacitors for leakage. You need to replace that capacitor.

As you can see from this http://www.mif.pg.gda.pl/homepages/f...10/u/UCL82.pdf the normal operation of a UCL82 is with -11.5V. (it will be a bit less than this as the screen is only 100V)

Good point the esr should not affect a 0.01uF capacitor very much and the high impedance of the grid should make this irrelevant to its operation. The -11.5V is for cut off, the valve in its quiesent state is at 0V and goes between the two for the negative grid signal, though the leakage cause a positive grid voltage and the valve to conduct too heavily and not operate correctly. I would still like to replace the UCL82 with a better one.