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Old 29th Mar 2020, 9:09 pm   #21
ajgriff
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Default Re: Ekco U353 Restoration

Yes. I used a cheaper version of Araldite but it's generally worked well in the past.

Alan
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Old 29th Mar 2020, 10:00 pm   #22
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Default Re: Ekco U353 Restoration

The attached highlights the joint which got damaged when my chassis fell. Just near to where the arrow on the left is pointing there's a circlip. It's a bit of a wild guess but I think if the lugs on the casing to the upper pot were released the top half of the pot would slide off the spindle. This would leave the casing itself in place but would allow access to the circlip. Removing the circlip might then enable the lower half of the pot to be withdrawn. Hope that makes some sense.

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Old 29th Mar 2020, 10:15 pm   #23
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Default Re: Ekco U353 Restoration

Yes Alan, you're right, the circlip retains the inner shaft, which is spring-loaded so that when its other end reaches the cut-out, it engages with the switch claws. I removed the circlip successfully but couldn't remove the innards from the rear pot, it wouldn't budge in any way. The brass knurled washer-kind-of-thing under the circlip may be significant but I can't work out how. Incidentally, when I put the two pots back together there was a certain amount of wobble between them which I cured by soldering two short lengths of solder braid between them as braces
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Old 30th Mar 2020, 12:15 am   #24
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Default Re: Ekco U353 Restoration

I've tried to zoom in on the previous image to show the brass thing with little wings in more detail as you may not be able to see much of it because of the upper pot's casing. As well as holding the upper shell in place I wonder if it unscrews? There certainly seems to be a junction between it and the washer with arms underneath. Someone who's dealt with one of these before might know.

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Old 30th Mar 2020, 10:30 pm   #25
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Default Re: Ekco U353 Restoration

I also thought maybe it would unscrew and gingerly tried a pair of pliers on it. but it didn't move. I think I'm going to leave well alone and just epoxy the switch back on. I'm sure there are items in the world that are more difficult to source than an 820k + 820k concentric pot with DPST switch. but I can't think of any at present..!
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Old 30th Mar 2020, 11:10 pm   #26
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Default Re: Ekco U353 Restoration

Quote:
Originally Posted by lesparapluies View Post
I'm sure there are items in the world that are more difficult to source than an 820k + 820k concentric pot with DPST switch. but I can't think of any at present..!
Blore Edwards would make one for you.

Ideally, it’s best to send the old pot so you get exactly the same style, shaft diameter (with/without flat), degree of rotation, log/linear law track, switch requirements, etc. They do have an online facility for you to specify your own parameters for a quote. I don’t know whether they’re presently open, but if so, Brett is very helpful in discussing and advising on your requirements.

Might be worth checking out their website:

https://www.blore-ed.com/

Every success in your efforts.
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Old 5th Apr 2020, 2:04 pm   #27
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Default Re: Ekco U353 Restoration

Thanks for the replies. The Blore Edwards option may be worth looking into when things get back to normal, I suppose the big issue will be whether the cost is worthwhile. I've hit a major snag in that the mains switch is proving very difficult to get working reliably - only one side of the switch works well, the other one is intermittent; have tried lots of things but I think basically it's just mechanically worn out. I could just bridge the other side and it would work OK but the safety aspect and sticking to the rules concerns me. I've attached a little circuit which would seem to be a possible solution and I'd welcome your opinions.
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Old 5th Apr 2020, 3:49 pm   #28
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Default Re: Ekco U353 Restoration

Quite a few live chassis valve sets had single pole mains switches.

Alan
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Old 5th Apr 2020, 8:35 pm   #29
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Default Re: Ekco U353 Restoration

Thanks Alan, I did wonder if I'm being too fussy.. I think I'm just going to bridge it for the moment, and if and when I get the set working I'll re-consider things on that front
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Old 26th Apr 2020, 9:08 pm   #30
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Default Re: Ekco U353 Restoration

Came across this capacitor in the radio, it's a coupling capacitor in the output stage. Value is 0.01uF but it seems to be electrolytic, in that it has a red and black end; "TCC Metalmite". That seems a very strange value for an electrolytic, virtually unobtainable, any advice please?
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Old 26th Apr 2020, 9:16 pm   #31
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Default Re: Ekco U353 Restoration

Not electrolytic. Can be replaced with a standard .01uF 350V polypropylene capacitor.

Alan
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Old 27th Apr 2020, 10:02 am   #32
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Default Re: Ekco U353 Restoration

The red/black marking might relate to which foil is outermost in the internal wind.
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Old 9th May 2020, 12:00 pm   #33
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Default Re: Ekco U353 Restoration

Thanks to everyone for advice so far. Spent a lot of spare time over the past 2 weeks or so rebuilding the power supply circuit, replacing the electrolytics and a few other caps, and also a few resistors. Most of the resistors in the entire set are about 25% higher than their stated values. I'm sure Alan will agree that the point-to-point layout of the circuitry is quite messy, and de-soldering components is difficult, especially from valve bases, where it's easy to damage the plastic surround with too much heat. Anyway, I plugged it in yesterday and it's working quite well on all bands. The wave change switch is very noisy and intermittent so will give that some attention. Regarding the remaining resistors, I suppose it's a choice of either leaving things as they are, or replacing the whole lot. One thing I would like advice on is the magic eye indicator valve (V4 on the schematic) I've no experience of these at all; this one lights up nicely but doesn't do anything apart from that. It seems to be fed from the audio going to the volume control, and all is as it should be, so should I assume a faulty valve? Thanks, Mark
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Old 9th May 2020, 6:18 pm   #34
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Default Re: Ekco U353 Restoration

Nice a bright it’s probably ok. As you tune in a station the length of the line will shorten. Its controlled from the AGC line, I.e, the DC output from the detector, a higher AGC -ve voltage will shorten the line.
On FM it takes the voltage across the 2uf capacitor in the discriminator circuit, the stronger the signal the higher that -ve voltage will be.
Check the resistors in the circuit of the valve then check if you have AGC voltage to alter the display.
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Old 11th May 2020, 10:21 pm   #35
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Default Re: Ekco U353 Restoration

Quote:
Originally Posted by lesparapluies View Post
I'm sure Alan will agree that the point-to-point layout of the circuitry is quite messy, and de-soldering components is difficult, especially from valve bases, where it's easy to damage the plastic surround with too much heat.
Agreed without hesitation. Worst thing so far was when I singed the tuning dial cord although it seems to be staying in one piece for the moment at least. Haven't got as far as observing the behaviour of the magic eye as I keep distracting myself (very typical I'm afraid) with other projects.

Alan
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Old 12th May 2020, 12:06 pm   #36
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Default Re: Ekco U353 Restoration

These exclamation mark tuning indicators are not as good as a proper magic eye. They were intended for battery sets but found their way into some mains operated sets. The filament (they are directly heated) is usually run from the cathode of the output valve in a mains set via a resistor....just a convenient place to pick up some 'free' voltage. As stated, the grid (if you can call it that....) is fed from the AGC line and should cause the line to shorten on a strong signal. I don't think the dot does much. Perhaps just check any high-value resistors associated with it.
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Old 20th May 2020, 11:09 pm   #37
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Default Re: Ekco U353 Restoration

Hello again, thanks for the last pieces of advice. The set is now working reasonably well. The magic eye doesn't seem to do anything spectacular, as previously observed. I'm a little bit doubtful as to whether the AGC line is working as it should.. FM stations are at all kinds of volume levels, from a very weak Radio 3 to an ear-splitting local commercial station (I appreciate that local FM stations tend to be heavily compressed but even taking that into account there seems to be big discrepancy). I've checked and replaced a few components in the AGC circuit; the 2M2 resistor was about 3M2 and the 470K was about 590K, but apart from that all seems to be OK, any suggestions as to what else to check, or should I just accept that it was a limitation of circuit design of that era?
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Old 20th May 2020, 11:20 pm   #38
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Default Re: Ekco U353 Restoration

Have you checked the actual voltage on the AGC line?

50s VHF sets generally aren't as sensitive as later transistor portables and need a good aerial. They were intended to be used with chimney aerials like TVs unless the signal was very strong. Presumably R3 is coming from Holme Moss, which is a fair way away.
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Old 21st May 2020, 7:22 am   #39
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Default Re: Ekco U353 Restoration

Manufacturers ref numbers.
On FM check the voltage across C49, on a strong signal it can get up to 40v, this is fed to the grid of the indicator via a 1M resistor R24.
On a similar chassis with a dipole tacked under the kitchen unit behind the radio the line shortens to about half its length on the main BBC stations and Classic FM.

If I get chance I will try and check what voltages I get.
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Old 21st May 2020, 8:39 am   #40
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Default Re: Ekco U353 Restoration

Ferranti U1032 which I believe is the same chassis.
Some voltages taken with a DVM to avoid loading the circuits.
Across C49 on FM
Classic FM -35v
Radio 2 FM -24v
Radio 3 and 4 are much less, could be the aerial I am using, when I had it on a loft aerial they were very similar, I only use it on Classic FM so not be investigating.
Junction R19/22/24
Classic FM -4.3v
Radio 2 FM -3.2v
This reduces the line length by about half.

Could not test LW too much interference.
MW Radio 5 Live -2.4v
Reduces just less than half length.

Hope that gives you something to work with.
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