Ekco (from Eric Kirkham Cole Limited) was a British electronics company producing radio and television sets from 1924 until 1960. Expanding into plastic production for its own use, Ekco Plastics produced both radio cases and later domestic plastic products; the plastics company became Lin Pac Mouldings Ltd. Although this is a large example of early radios I felt the need to have one in my collection. It cost 24 guineas when new equivalent to £1613 today, so only for the rich. You often find this design on the cover of many tribute books to old radios. A five-valve domestic receiver in an Art Deco Bakelite case featuring large circular tuning scale around a metal speaker grille depicting a treescape.
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| Factory photo of hinged moulding used in making of my cabinet |
The SH25 was the first superheterodyne radio made by E K Cole and Co Ltd. In 1917, Edward Howard Armstrong (1890-1954) developed the superheterodyne electronic circuit, which significantly improved the sensitivity and selectivity of radio receivers over a wide range of frequencies, making amplifier tuning unnecessary. This made the task of tuning the radio receiver to different stations much more simple and straightforward. Radios with superheterodyne circuit technology are commonly known as ‘superhets’. The design was one of the architect, J.K. White and was the 3rd model using this cabinet including a DC mains version, starting as far back as 1929.
My example had laid in a garden shed for many years and was water damaged and quite rusty so I'll divide the repair into eight chapters devoted to individual restoration areas starting with the loudspeaker.
1: The speaker repair
I thought at first the speaker & it's driver transformer was a complete write-off, but after removing it and checking the four winding I found continuity in all four to my great surprise, considering the amount of rest. But the all the frame was rusty and the front was completely engulfed in dead spiders and their old cocoons. The cone and coil were jammed solid and the card surround was also ripped. This is also the first time I've come across a loudspeaker without a fixed magnet, instead it uses an electronic one, L20 known as 'field coil' with a resistance of around 2.5 k ohms. The whole thing comes apart by removing a hex bolt in the center front of the speaker cone. The rear coil then falls away, take care not to break the field coil wingdings and spacer washers.
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Speaker with transformer removed showing field coil on left and cone coil connector on right (extra tag is for the hum coil in series tucked b/w the two.
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| The field coil around the hex bolt fitting |
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The rear of cone showing the damaged areas. take care not to wobble lose wire too much or they will brake.
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Cleaned and clear Aroldite applied to repair paper
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Also remove the speaker transformer with it's two fixing bolts, taking care again not to damage the speaker winding wires, unsolder where necessary and take photos of the connection strip (I've included a diagram I made of mine here) I used a car vac to remove all the webs and spider debris, also a bronze wire brush fitted to an electric drill to remove rust. I then painted the cleaned areas with
Hammerite Kurust that is very good for this sort of a job, it will leave the steel with a black coating that will keep the oxygen away and stop future rust.
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Before and after views of 90-year old speaker, I couldn't save the label, lol |
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Large value capacitors for HT smoothing were were expensive in the early days of radio and a neat trick used in this speaker was to fit a
'hum eliminator coil' in series with the secondary winding of the transformer, it is a few turns of thick wire located between the 'field coil and the chassis of the speaker in the same magnet plain as the field coil. The rip in the cardboard cone I rejoined with clear Aroldite making sure the cone was still aligned correct.
- Sound output transformer, 5 pin terminals from left to right
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- 1- Electric magnet winding (yellow wire)
- 2- primary winding (500 ohm) (red & white stripes)
- 3- N/C
- 4- primary winding (500 ohm) (red wire to HT)
- 5- -ve (earth) black wire
- (secondary winding on rear 0.5 ohm + hum coil in series)
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Wide view of the stripped down Ekco with speaker removed, the pile of valves at rear all all from the 1920s that I found in an auction
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The speaker moving coil in place with magnet removed. A frame is fitted to the front to hold hex bolt
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The 4 wires to the the rusty transformer, see wiring diagram I made if unsure where they go
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| Speaker after repair and rust paint applied |
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I've included lots of photos of my repair, this type of speaker is quite rare now and worth restoring and later types are quite expensive these days. The picture below just shows how these things can be restored, yes it does take time, but all restoration work can be quite time consuming, but rushing the work is bound to end in tragedy - so take it slow
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| What I found behind speaker cloth - shock horror |
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| Bakelite press being installed at Ekco's factory in 1932 |
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2:Power Supply Repair
The power supply uses a Westinghouse metal rectifier used under licence to Ekco by the American company as displayed on a metal plaque on the rear of the set. This had totally gone rusty on it's heating fins and also there was evidence of sparking at one end in the form of holes. These type of units when faulty give off a nasty smelling toxic gasses, so I decided to override them with modern silicone equivalents. All the paper originals in my case were open circuit, so I used their existing terminals for the wiring of new stuff, but this might not be need in your repair.
The mains transformer has 4 secondary wires, 2 supplying HT at
210v AC and 2 feeding the valve heaters at
4 v with a 5 amp rating, each valves draws 1 amp wired in parallel. The 2 HT wires feed 2 silicon diodes via 2 x 2 uF paper capacitors (C25-26) working as a
voltage doubler circuit. Because the Westinghouse originals have a high forward resistance some extra resistors need to be added to reduce the voltage by about 70 volts. I did a bit of ohms law calculations and came up with a total of 200 ohms needed using 20 watts of power.
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New load resistors and diodes fitted to a panel and held down by an 'L' bracket using existing bolt. |
remove AC wires from Westinghouse, attach here |
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Some early wiring diagrams show the Westinghouse diode polarity the wrong way around, this is because in those days they thought the current flowed from the Anode to the Cathode, but more recently it's been proved it's the other way. So my diagram is correct, otherwise you'll get -ve HT voltage, remember the Cathode is the painted end of the silicon diode. My resistors are quite close to the Bakelite cabinet, so I glued some tin foil to reflect heat away from cabinet. When switch on the HT was low and the large 8uF electrolytic was getting hot quick, so I quickly cut away the 3 red wires attached to it (Gorilla taped over them) and fitted a modern 32uF 450v across my mod panel for ease.
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| 1932 Wireless World page |
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| Quick reference drawings |
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3:Sound output stage repair
We now have HT and heaters, but no sound from the volume control (using a test signal) so check anode & screen voltages on the two stages. All good there, but 300 v in the grid of the output valve is a little strange. I remember reading an on-line repair that a guy did on one of these sets in 1992, he thought at the time he had the only working one in existence, lol There's at least two now. Anyway he said that the driver transformer was shot in his set. So I thought "let's check the winding's on mine", no easy to get at as it's mounted on a sub panel, it turns out that the input winding is o/c and not only that, it's collecting 300 v internally from somewhere? That was put right by cutting the wires away from the panel and soldering 3 new wires to a donor transformer I fitted topside where there was enough room for it, the 4th wire was earth so I just earthed it at the other end with a solder tag to chassis. The ratio of the new TX was 5:1, in the old article I read from 1992 he just coupled the valve with a capacitor from the previous stage, but that comes at a 5:1 loss of volume. Luckily I have a few of these inter-stage transformers in my spares box, as I buy old parts on line regularly, I love the Net. Before the Net came along repairing stuff was an expensive nightmare.
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| The Lissen used inter stage transformer to replace o/c one underneath - raised on a spacer bracket over a trimmer screw |
4:Speaker cloth replacement
While I ordered the paper capacitors for the power supply (florescent lighting types are great) I removed as much of the rust from the chassis and ordered a yard of speaker cloth that I thought would look nice, dress making cloth is just as good as purpose made expensive stuff, you can order test samples for a £1 and the yard I chose was an extra £5. The front brass comes away easily with cloth by removing 6 brass hex nuts, one was missing I ordered a new one on line costing £1.50. A circular spring loaded ring or loop holds the cloth in place, you'll also need to bend back some copper fold overs, careful with these they are soldered in place and can fall off. The loop or ring was rusty, so I cleaned that with wire wool and painted it with rust remover too.
The material I decided on was a red 3D brick effect, giving a glow of rays to a Sunset, taking care to arrange the pattern so it's level like bricks would be in a wall. I lived with it for a few day using the slightly too small sample and decided I liked it. I toyed with the idea of polishing the brass front, but decided in the end as it was nearly 100 years old, it would be classed as an antique soon, and like my friend Dave Rimmer commented it would lose it's original patina. I suppose any form of cleaning does that, you just need to not over do it. The brass had been anodized, this preserves the colour by makes it brownish. A light rub with oil brightened that up.
5: Oscillator coil repair
My next check was that all the 3 RF valves had anode & screen voltages, V2 the oscillator valve had only 100 v, should be around 150V, a preset resistor feed R1 aloud me to adjust that to the correct voltage. I also found there was -7.5 volts on it's input grid and considering it's decoupled to chassis vial 10 ohm oscillator coil I thought that was a bit high, you guessed it the coil was open circuit.
You won't find an under chassis layout on-line, so here's one I made for you, mind you the cobwebs have been removed and it had a good vac over. Always take a picture before you clean in case wires drop off.
Back to the coil repairs, I removed the bolt from the top of the coil and removed the screening can, this relieved all the winding inside and the solder terminals, a quick check with my test meter showed me the 2 terminals that fed the open winding. Sadly the wires hadn't just come lose so a new coil or winding was needed. A new coil was the option I chose I would wind a new one and just drop it over the faulty one. For the coil former I used a sticky tape center that was large enough to drop over the existing coil then I roughly calculated the thickness of the wire and the size of the winding, exact accuracy is not needed, I rolled the wire on double sided sticky tape for ease of winding.
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| Oscillator coil with screening can removed (top arrow shows o/c winding - bottom arrow shows o/c terminals) |
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| New winding just dropped into place over existing one and wires soldered to terminals |
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The nice thing about this repair is the size of the coil, almost a big as a valve, giving lots of room to repair. After this I just had to repair the aerial coil, I had accidentally caught a solder tag & it's wire with my rush removing drill, all was well I just looked at my first photo and that showed me where the wire went. It was underneath the chassis support triangle bracket, out of finder reach, but all was not lost I recovered the broken copper tinned wire from inside the coil and made a new fixing hole where I could get at it. (you can see the new position by the white arrow on the under chassis photo above.
6: Band switch repair
This was completely seized and needed a little bit of attention. Again the size of this unit is impressive and all open so can be cleaned without removal. It uses a shaft with rotating cams that just push two brass contacts together, I applied oil to the shaft and the cams and it started to turn again, while rotating I could see some of the terminals didn't move, these were the ones that needed re-bending towards the cam. Care is needed not to over bend, a cleaning brush can be applied while closed to ensure both contacts on each switch are cleaned. It's a 3 position switch LW MW and GRAM, when gram is selected the two plugs at rear marked gram are connected to the output stage, unfortunately on the wrong side of the volume control, so it will be at full volume in gram mode. If your thinking of adding Blue Tooth, not a problem as volume can be adjusted on the MP3 player.
Wish the oscillator stage and audio output stages now working I can now at last hear radio signals on both bands, although the Local Distant switch doesn't do anything.
7: Local/Distant Switch repair
This is a mains voltage type rated switch and is found at the rear of the volume control. It was jamming and the rear was loose, so I decided to remove it and clean it up. The volume pot assembly is held by a traditional large hex nut with 2 capacitors and 5 wires, that were photographed and then un-soldered. The rear is held in place by two clips either side that can be prized apart. While inside it may be worth oiling the volume track (don't over rub as it may crumble)
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| 'A' shows the rear of the volume pot and the off center pin that moves when in slot a spring loaded contact lever - the contacts 'b' & 'c' can be cleaned after removing a card dust cover |
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| The local distant switch located behind the volume control. The switch itself had HT on it, as it shorts out an IF transformer to reduce signal gain. |
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The reason in my case that the switch was o/c was because a body of a spider was jammed between the two contacts and had to be scraped away to make it work again. All that's left now is cosmetics.
8: Cosmetic repairs and extras
In my history of radio repairing I like to add a personal touch, using in the way of dial lights. No lights were used in the original design, probably because not much room left after speaker and clock dial were fitted. I decided to cut 4 slots into the 1 inch thick speaker baffle and just leaving the glass part of the bulbs showing, even then the bulb light was in-your-face, so a carefully cut 4 leather triangles and Aroldited them to the brass surround.
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| Four recesses cut for the 3volt miniature railway bulbs wired in series |
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| Gorilla tape used to hold wire loop and bulbs in position fed by 12volt transformer |
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| Final test so that pointer didn't hit the bulbs |
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| Power fed to TX via white wires to AC inside & two black wires to 12 volt bulb loop 4 x 3 v in series = 12v |
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| Final picture showing leather triangles fitted to hide glow of lights |
9: The Back and Mains plug
As with most old mains cables they get thrown away and the average cost on-line of an old 2 pin Bakelite plug is around £20. I found that the socket size in a modern 3 pin extension socket is the right size but the gap is larger. So the trick is to use a small square of wood, drill two holes with the correct spacing for the socket on the set and feed the cable through a smaller hole on the rear. Solder or push seal the connections to the brass sockets, finish off with Gorilla tape to insulate the whole thing. Not safe by today's standards, but as good as original. The cloth to cover the vent holes was taken from the old speaker cloth cut into 4 quarters and glued
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| The original back to the set was water damaged with the inside and outside piece of plywood falling away, so I removed them. The back was still thick enough to re-fit, but had also warped quite badly |
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| Restored back with brass plated re-fitted over newly painted rear |
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| Small block of wood cut to fit sockets in from another similar socket |
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| Finished off with Gorilla tape to hide wires and painted brown |
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To remove the warps in the back I used a hot iron on an ironing board, after PVA glue in any loose pieces. The final job is to clean the outside of the Bakelite cabinet, because the boxed sections have a textured look this has protected the set from being scratched, also the slight slop on the top has not allowed objects to be placed on the top (flower pots, drinks etc.,) So I cleaned most of the grease and furniture polish away with a toothbrush and modern kitchen cleaner spays. After you'll find a dull almost cloudy look to the cabinet, this is caused by the cleaners removing the oil from the Bakelite, so now is the time to add some new oil, I used linseed oil, it may need two coats to bring back the sine again. The total repair took about 1 Month, devoting a day almost to each chapter, cosmetic stuff can be done while ordering parts. For the numbers collectors my
serial number is SC 11424
It was a great project and I'm sure I will need to update the Blog as time goes by and other things fail, but for now she's fine, 90 years is a long time with out love.
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