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Old 5th Mar 2023, 9:22 pm   #1
Johnnyyork
Diode
 
Join Date: Feb 2023
Location: York
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Default Help with Ekco A733.

Good evening everyone.
I've just bought my first valve radio. I was desperate to get hold of one and finally one popped up on marketplace and I rushed off to collect it. I now have it opened up on my dining table and have been inspecting it and scratching my head for a few days now. I am but a simple plumber and have very little previous experience with electronics but this seemed like it would be a fun hobby for what little spare time I have on an evening.
So I have a few questions if any of you pro's out there have a minute to spare. The set is an ekco a733 which I now know to be an export set and I can't find a schematic online anywhere so I'm thinking to just replace the capacitors, fire it up and hope for the best. I don't have a lot of equipment, just a multimeter, soldering iron and some hand tools.
I'm wondering how many capacitors I should change. There's a big TCC electrolytic can on the top, it looks healthy enough but I've read that it can still be faulty even if it looks ok. Would it be wise to change that before I switch it on?
Also there are a couple of colour coded caps and I've looked at the chart to try and determine what value they have but it seems they are missing a 5th stripe that would give the voltage limit, or am I just reading it wrong?
Thanks lads for any help offered, I really appreciate it.
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Old 6th Mar 2023, 2:44 pm   #2
cathoderay57
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Default Re: Help with Ekco A733.

Hello and welcome to the Forum. The closest schematic that I could find is the Philips B5CA37A that uses exactly the same valves. There will be differences in the circuits but it might be some help. It's on the Radio Museum website here https://www.radiomuseum.org/r/philips_b5ca37a.html. You can download it free as a guest user. You might find this link a useful resource, especially concerning your question about capacitors https://www.vintage-radio.com/repair...and-tests.html. If the Philips circuit proves to be a reasonable match then let us know and we should be able to give you some pointers as to which capacitors to focus on initially. From what I can see from your images, the colour coded components are resistors. Colour-banded capacitors certainly exist but I couldn't see any in your set. Best of luck, Jerry
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Old 6th Mar 2023, 3:13 pm   #3
Mr 1936
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Default Re: Help with Ekco A733.

Hi

Colour coded capacitors are quite rare, and those you might encounter are usually of a type that does not degrade or need changing.

Your last photo shows a resistor, which is Orange, Orange, Orange, Silver. That means it is Three, Three and Three zeroes i.e. 33000 ohms or 33 kilohms. The silver means that the tolerance is plus or minus 10 %, so it could be anywhere from 29700 to 36300 ohms. Resistors are generally reliable but types with a value greater than about 470 kilohms can go high in value.

Opinions differ on the need to change capacitors, and there are no hard and fast rules. The reason to change the smaller valued types is that the waxed paper dielectric inside very slowly absorbs moisture over the years and they become electrically leaky. In certain circuit positions this leakage risks damaging other components or spoiling performance, so its best to change them straight away. In other positions the leakage is not so critical, and they can be changed one at a time after the set has been got going.

Much smaller value capacitors used mica or ceramic inside, these are generally reliable and can be left alone. (Even if dipped in wax, the working parts inside don't use waxed paper !)

Larger valued types known as electrolytics can also degrade over time, and it is common to change the biggest of all (shown in your picture as 50-50 uF) which is the main HT smoother. This is actually two capacitors sharing one can, with a common ground connection via the can metal. Electrolytics are usually larger in value than 1 uF and have a metal can, sometimes with a cardboard sleeve. They also have a unique symbol on the schematic.

When looking for replacements, be aware that standard values tend to be 22 uF, 47 uF etc rather than the older 25 and 50 uF. This is of no consequence, as the tolerance was often plus or minus 20% because the exact value was not critical.
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Old 6th Mar 2023, 3:57 pm   #4
dazzlevision
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Default Re: Help with Ekco A733.

The Ekco A733 is an export market radio (although made in the UK by E K Cole Ltd, of Southend-on-Sea, Essex), having Medium and several Short Wave bands.

You might find it more difficult to locate a circuit diagram or full service information as a result.

See post 86 in this thread:https://www.vintage-radio.net/forum/...=111407&page=5
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Old 6th Mar 2023, 4:39 pm   #5
Gabe001
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Default Re: Help with Ekco A733.

The first step imo is to build a lamp limiter. This acts as a current limiter, preventing damage in case of leaky capacitors, and also can be used to reform the electrolytic capacitors.

As a very broad rule, non polarised capacitors between 0.001 microfarad (1nf) and 0.22 microfarads (220nf) will need replacing. These will be those nasty black hunts and the metalmites. The hunts will probably disintegrate on contact but should have the value printed on them. If you can get a schematic with an underchassis view it will help you lots.

The electrolytic capacitors which are the polarised capacitors may or may not be ok. It's your call but if you cannot reliably test for leakage you may want to replace for peace of mind.

A good starting point is to do a few checks on the mains and output transformers (resistance of windings and resistance to chassis), replace the grid coupling cap (known as 'that capacitor', see sticky thread) and switch on via the lamp limiter, monitoring the electrolytic caps for heat. Then replace one capacitor at a time and check your work in between.

There's a recent thread by Tonyekco who is a new starter like you and who has been asking the same questions. Have a read, you'll find it useful

https://www.vintage-radio.net/forum/...d.php?t=198443

Good luck
Gabriel
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Old 6th Mar 2023, 4:48 pm   #6
Gabe001
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Default Re: Help with Ekco A733.

This may help.
Capacitors with orange marks will need changing. The ones in blue may be ok.
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Old 23rd Mar 2023, 9:58 pm   #7
Johnnyyork
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Default Re: Help with Ekco A733.

Hi guys.

Sorry for the late reply, I haven't had chance to do anything since posting my question here but tonight I may have a couple of hours...baby is asleep, wife is out and radio is back on the dinner table. Thank you all so much for your replies.

Thanks Jerry for the link to the Philips schematic, I will download it and hopefully I can see if it is similar to my radio. I'm also glad the colour coded ones are resistors and hopefully don't need replacing.

Thanks Mr 1936, thanks for the advice. I think I will change the HT smoother just to be on the safe side, that's the one that can cause a lot of damage if it fails, right? I presume I wouldn't need to use 2 capacitors to replace it, I could simply use a bigger one?

Thanks dazzlevision for the link. It mentions that the A733 may be similar in circuitry as the A731 although I see that the A731 has 7 valves and mine has 6, four of which are the same but they have 3 which are different.

Thanks Gabe for your input. I've noted all the caps you marked as best to change and I think I have bits in the loft to build a lamp limiter so I'll give that a go. Does the build act as a fuse? Also I will check the transformer but to be honest, I don't really know what I'm doing. I will watch some YouTube videos and hopefully that will show what to do.
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Old 24th Mar 2023, 9:45 am   #8
cathoderay57
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Default Re: Help with Ekco A733.

Quote:
I presume I wouldn't need to use 2 capacitors to replace it, I could simply use a bigger one?
Nope, the twin capacitors in the can are there for a purpose and must be replaced individually. Jerry
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