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Old 24th Aug 2016, 9:34 am   #1
lloydwells
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Default Ekco 313AC. Hum.

HI I have an Ekco 313ac that's probably not been used in 40 years I followed the advice of giving it a once over checked all the caps and resistors that weren't buried in big tin boxes and slowly warmed it through with a lamp limiter. It works to a degree stations are received but the background hum is terrible I have managed to download a schematic for it but no component values HELP. The hum seems to start the second its turned on as a mechanical vibration in the set and then come through the LS when the set has warmed up. Any help greatly appreciated.
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Old 24th Aug 2016, 10:02 am   #2
Edward Huggins
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Default Re: Ekco 313AC. Hum.

Could be the laminations in the mains transformer and also the smoothing/reservior caps when warmed up. Edward
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Old 24th Aug 2016, 10:47 am   #3
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Default Re: Ekco 313AC. Hum.

As far as I know this is a mains powered TRF set. If it has a balance control, have you tried adjusting it?

If you can post some pictures and maybe the circuit, this may enable us to identify the smoothing capacitor/s
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Old 24th Aug 2016, 12:10 pm   #4
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Default Re: Ekco 313AC. Hum.

http://85.144.220.212/nvhr/Ekco_313AC.pdf

Luv the rectifier.

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Old 24th Aug 2016, 12:15 pm   #5
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Default Re: Ekco 313AC. Hum.

Hmmmm. Obviously PNP valves in that set
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Old 24th Aug 2016, 12:51 pm   #6
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Default Re: Ekco 313AC. Hum.

Ok it has what Ekco refer to as a hum control basically a variable resistor fitted to the back of the chassis this has been adjusted so as to minimise the hum as much as possible bit it's still dreadful. I'm struggling to find the mains filter cap unless it's the big tin box up the far corner of the chassis. It's still running with the original metal rectifier I'm wondering if this maybe isn't working correctly? Or possibly if it's something to do with chassis grounding as it's significantly better with the earth attached but still flippin awful.
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Old 24th Aug 2016, 12:52 pm   #7
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Default Re: Ekco 313AC. Hum.

Personally speaking, I would not have applied any mains power to it until the set had been thoroughly checked through, to say the least, more damage can be done by applying power to any apparatus like this before smoothing caps and the like have been checked, in most cases all of the capacitors would have dried up and certainly gone extremely leaky.

Best wishes

Ken
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Old 24th Aug 2016, 12:59 pm   #8
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Default Re: Ekco 313AC. Hum.

Quote:
Originally Posted by lloydwells View Post
I'm struggling to find the mains filter cap unless it's the big tin box up the far corner of the chassis.
Where do the wires from it go to?
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Old 24th Aug 2016, 1:26 pm   #9
ms660
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Default Re: Ekco 313AC. Hum.

Some photo's might help, chassis top and underneath.

Lawrence.
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Old 24th Aug 2016, 1:48 pm   #10
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Default Re: Ekco 313AC. Hum.

It won't be the rectifier but yes both smoothing caps (the one after the rectifier and the one across the hum control) will be in the box likely values 8 or 16 uf. Disconnect their HT wires and connect temporary ones.
All the caps in that box will need changing if you intend to use the set.
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Old 24th Aug 2016, 2:53 pm   #11
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Default Re: Ekco 313AC. Hum.

Ekco made a TRF, model RS2 AC, the next year (1931) that uses the same valve line up as your set. The circuit has similarities but is not identical to your set. The circuit has component values marked and so it may be useful to get an idea of some of the circuit values in your set.

http://www.service-data.com/product....24/2158/s11524

Note that the page I have linked to says "No Circuit Diagram" but this is in error.

Last edited by ukcol; 24th Aug 2016 at 2:55 pm. Reason: spelling
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Old 24th Aug 2016, 3:12 pm   #12
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Default Re: Ekco 313AC. Hum.

Hi LLoyd

Sorry not got access to my cleaned up version right now, here is a copy of my original scan

Cheers

Mike T
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Old 24th Aug 2016, 3:18 pm   #13
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Default Re: Ekco 313AC. Hum.

That is bloomin fantastic thankyou
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Old 24th Aug 2016, 3:19 pm   #14
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Default Re: Ekco 313AC. Hum.

Spot on.

Lawrence.
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Old 24th Aug 2016, 3:34 pm   #15
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Default Re: Ekco 313AC. Hum.

Don't get phased by the way the resistors are marked.

The ω symbol is used for Ohms and the Ω for MegOhms

I have seen this on a number of early diagrams and its obvious when you look at the position of the components.

Cheers

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Old 24th Aug 2016, 9:55 pm   #16
lloydwells
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Default Re: Ekco 313AC. Hum.

Pleased to report now cured. I had actually been all over the thing with a meter checked all the capacitors but without a marked diagram I could only really be sure of the ones that had values stamped on them. The filter cap tested at 6.4uF and appears to be fine although I will replace it. However the decoupling caps in the big can were reading between 4 & 8 uF and the decoupling resistors had... well I think drifted is somewhat under selling it. All now replaced and we have a happy Ekco.
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Old 25th Aug 2016, 9:25 am   #17
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Default Re: Ekco 313AC. Hum.

Well done Llloyd, it makes it all worthwhile when you achieve your goal.

Ken
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Old 25th Aug 2016, 4:43 pm   #18
Cobaltblue
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Default Re: Ekco 313AC. Hum.

Happy EKCO's are the best kind so well done Lloyd, my 313AC was restored almost 25 years ago probably needs doing again

I suppose at the same time I should look at my 313DC which I bought incomplete as a spare case for my second 313AC, but when I discovered it was the DC version that idea was canned.

I did upload the 313DC circuit to Radiomuseum I ought to upload some pics

Cheers

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