Ekco A455

[sexton_mallard]

I was given this nice little tranny which was used in butchers shop on Canvey Island. following a deep clean the blood spatters remain impregnated into the (formerly off white) grille cloth.

After a quick safety check and remounting the tuning gang on new rubber washers, the set was 'woken up' gently over a few hours. iI now have good reception on LW and MW but lacking volume. The volume fully open is still quiet even when flicking the wavechange switch or probing the chassis. The sensitivity is good and the sound quality also good and undistorted. A quick power supply check shows 21V DC.

I'm now focussing on the audio output stage. has anyone come across this before on this type of set? The on-off volume control does not switch off and the volume control works as expected.

[Nuvistor]

I don't have circuit with me but if this radio uses the Mullard RF/IF module with AF117 transistors it would be worth checking if the output was sufficient.
Electrolytic audio coupling caps are another possibility.
Frank

[Nuvistor]

I have had a look at the circuit and it does use the AF117 series transistors in a Mullard module LP1156.
I would check the output of that module to make sure there is enough drive for the audio stage.
The on/off switch is either stuck in the on position or been shorted out at some time, replace it.

[marconi_pete]

As the set uses AF117 transistors, I'd change them for AF12x transistors. Those AF117 transistors are prone to developing tin whiskers inside the can creating internal shorts. Best to replace them for peace of mind later down the line. I suspect the output transistor may be at fault so that would be the first place iI'd look.

[sexton_mallard]

Just an update. I had the set on tonight on full voltage and up to now there was a noticeable but not excessive 'mains' hum. This began to get louder and louder so I switched off! I will check the gold 500mfd smoothing electrolytic before delving any further.

On the subject of AF117 tin whisker disease, I take it the effect is pretty much a hard s/c as opposed to degraded performance? My bush TR82C is in good health and I can see 3 of them with the back off. Now I know what to check first if the set decides to stop working

[Nuvistor]

I have had the AF11x series cause degraded performance as well as no output.
The hum, if the output transistors start to draw excessive current they can cause a loud hum.

[marconi_pete]

Those AF117 transistors don't always go short circuit. I've had some sets with degraded performance caused by faulty AF11x transistors. In this situation I'd suspect the output transistor.

[sexton_mallard]

I returned to this little butchers shop radio tonight. I noticed the 16 mfd coupling cap (C22 on trader sheet 1819) from the IF module to the volume control had a nasty brown stain on one end... I snipped it out - it was dead! I popped in a 22mfd electrolytic and success . Lots of the right sort of noise blasting out of the speaker. Now to get a replacement ganged volume/switch and a new power lead in next.

[Nuvistor]

I remember selling these sets,the first time I took the back I thought were is the rest of it, lots of fresh air inside but it allows a bigger speaker.
I have the identical looking valve versions, a bit more inside those.

Glad you fixed it, nice little radio.
Frank

[sexton_mallard]

Thanks Frank. To me this set is the transition from valve to (gemanium) transistors. Here is a picture of the beast. its a bit battered and discoloured from its career in the butchers shop but it scrubbed up well, especially the grille cloth which was removed, washed and replaced with Maplin aerosol glue.

[Herald1360]

Did it need biological detergent?

[sexton_mallard]

When I extracted the baffle from the cabinet, the speaker mounting screws backed themselves out causing 'pooks' in the grille cloth when I unscrewed the speaker retaining nuts I decided to attempt to remove the cloth which peeled away cleanly with no problems. I then wound the screws back in with a bit of Loctite.

SHMBO worked in the 'rag trade' and did some work as a conservator in the National Trust... I handed the filthy cloth over to clean. The cloth was soaked in a lukewarm plain water solution for about 20 minutes. It was then removed and placed face down on an old towel. A weak solution of Vanish stain remover and bleach was made up and the back of the cloth was patted with an old soft toothbrush dipped in the solution. This had the effect of pushing the dirt out into the old towel.

After a few rounds of dip-dabbing, the cloth was again rinsed in warm water and left to dry. I was pleased to note no shrinkage or expansion took place, and I remounted the cloth using Maplin spray glue. The end result you can see in the previous posted picture.

[Herald1360]

Has an AF117 died now?

[sexton_mallard]

Originally Posted by Herald1360

Has an AF117 died now?

Not yet! This interesting little set has been in daily use since working from home but the mains hum was getting more intrusive. I treated it to a replacement mains smoothing capacitor, a 680mfd 35v to replace the rather attractive yellow 500mfd cap which was down to about 300mfd on my tester.

[Nuvistor]

I like the look of this set and the valve version, just like the style.

And where did those 5 years go from when you last posted about the A455, time slips by.

[sexton_mallard]

Originally Posted by Nuvistor

I like the look of this set and the valve version, just like the style.

And where did those 5 years go from when you last posted about the A455, time slips by.

Tell me about it. The good thing is this set and many others have been relatively reliable in that time. I have 3 sets with AF117s and none have failed...so far. I like these series of Ekco sets as well and hope to get a few more especially the valve version.