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Old 20th Aug 2019, 9:00 pm   #1
trabant
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Default Ekco 313AC problems

Hi I have an Ekco 313 AC obviously hovering around the 90 year old mark . When turned on the set lets out a wap wap wap noise which gets progressively quicker till it goes after about 30 seconds at this point it will tune strong stations but no amount of fiddling gives much in the way of volume there's a steady background hum but not that bad it has the mains energised external speaker the tuned station is also fairly distorted.
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Old 21st Aug 2019, 9:14 am   #2
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Default Re: Ekco 313AC problems

Does sound like it's time for a capacitor check. Wap wap wap could be motorboating caused by bad HT decoupling.
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Old 21st Aug 2019, 5:31 pm   #3
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Default Re: Ekco 313AC problems

Does this also.explain the distortion and lack of volume.
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Old 21st Aug 2019, 9:18 pm   #4
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Default Re: Ekco 313AC problems

I would agree, instability of any kind can point towards decoupling capacitor failures, and considering the age of the set this is likely, assuming it hasn't been recapped recently.
Alan.
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Old 21st Aug 2019, 9:32 pm   #5
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Default Re: Ekco 313AC problems

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Originally Posted by trabant View Post
Does this also.explain the distortion and lack of volume.

Not necessarily, but it's probably going to need to be fixed before attempting to deal with that in itself.
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Old 22nd Aug 2019, 7:44 pm   #6
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Default Re: Ekco 313AC problems

It wouls be a good idea not to run it again until the caps have been checked/ changed or you may suffer expensive damage to othe parts.

Ed
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Old 23rd Aug 2019, 2:48 pm   #7
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Default Re: Ekco 313AC problems

I have changed the smoothers still lacking volume and distorting
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Old 23rd Aug 2019, 5:35 pm   #8
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Default Re: Ekco 313AC problems

Has it stopped motorboating?
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Old 23rd Aug 2019, 6:20 pm   #9
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Default Re: Ekco 313AC problems

Yep we've packed that in
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Old 23rd Aug 2019, 6:46 pm   #10
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Default Re: Ekco 313AC problems

More vital are any anode / grid coupling caps.

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Old 23rd Aug 2019, 7:46 pm   #11
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Default Re: Ekco 313AC problems

There's a circuit in Radiomuseum, but no component values. And the rectifier symbol is the wrong way round!


It's just about legible in the thumbnail view if you can't wait for the download.


Volume control looks like it's by variation of the RF amp screen voltage. Other "oddities" are a tapped choke and series resistor in the negative supply which provide bias voltages for the valves. The detector/first AF valve has zero bias in radio mode but picks up some negative bias from the bias chain via the pickup coil if a period gram is plugged in.


Is the metal(?) rectifier OK? Is the speaker field provided by a separate supply- it can't be fed from the mains as suggested in the RM circuit. Or is that negative choke the speaker field?
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Old 24th Aug 2019, 11:06 am   #12
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Default Re: Ekco 313AC problems

Schematic...W.W. Jan. 1931 mag page 19:

https://www.americanradiohistory.com...ld-1931-01.pdf

Lawrence.
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Old 24th Aug 2019, 11:33 am   #13
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Default Re: Ekco 313AC problems

Right the speaker is fed mains from a.socket on the rear of the chassis the speaker contains one of those good old fashion boxes of bitumen full of caps these are all about two years old it also has its owns selenium rectifier . Both this rectifier and the one in the set work fine .
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Old 24th Aug 2019, 12:20 pm   #14
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Default Re: Ekco 313AC problems

Quote:
Originally Posted by ms660 View Post
Schematic...W.W. Jan. 1931 mag page 19:

https://www.americanradiohistory.com...ld-1931-01.pdf

Lawrence.

Looks like where the one on Radiomuseum originated!
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Old 25th Aug 2019, 1:23 pm   #15
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Default Re: Ekco 313AC problems

The circuit has some similarities with the schematics on the M23 service sheets.

The Broadcaster and ERT service sheets have component values and voltages but I did spot some errors.

I would try to use the radio with another permanent magnet loudspeaker just in case the existing energised speaker is faulty.

The M23 has an 8uF reservoir capacitor, 2uF smoothing cap and two 1uF bypass capacitors.
One is connected to the screen grid of V1.

The equivalent capacitors on the 313AC receiver should be changed.

The 0.004uF capacitor across the HT winding of the mains transformer should also be changed.
Use a 1kV capacitor if possible.
Are you using a 'mains' aerial?
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