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.

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.

Re: Ekco 313AC problems
 

Does this also.explain the distortion and lack of volume.

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.

Re: Ekco 313AC problems
 

Not necessarily, but it's probably going to need to be fixed before attempting to deal with that in itself.

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

Re: Ekco 313AC problems
 

I have changed the smoothers still lacking volume and distorting

Re: Ekco 313AC problems
 

Has it stopped motorboating?

Re: Ekco 313AC problems
 

Yep we've packed that in

Re: Ekco 313AC problems
 

More vital are any anode / grid coupling caps.

Ed

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?

Re: Ekco 313AC problems
 

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

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

Lawrence.

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 .

Re: Ekco 313AC problems
 

Looks like where the one on Radiomuseum originated!

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?