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Old 24th Aug 2010, 3:59 pm   #1
Radio_Dave
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Default 1931 Ekco M23

Here’s my restoration of a 1931 Ekco M23 3 valve TRF. It was very quickly apparent that it had been kept in very damp conditions. The chassis was very rusty, the speaker cloth had mildew and the speaker baffle board had rotted, allowing the speaker to fall out! The plywood back was missing, presumably rotted away too?

Chassis
After dealing with numerous creepy crawlies and cobwebs the restoration started by stripping down the chassis. All components, apart from coils and windings, were washed in soapy water. Everything came up really well. Even the cloth covered wire was serviceable

The metal chassis was made up of several parts, all riveted together. After drilling out these rivets the parts were stripped (yes the chassis was originally painted). All metal parts were then submerged in oxalic acid, for 12 hours, until the rust was removed. I used Humbrol, number 11, enamel in an airbrush to paint everything and the chassis was then reassembled with 6BA nuts and panhead bolts

The mains transformer had rusty laminations. I didn’t want to use any kind of chemical remedy, so I used a brass wire brush, to get rid of the majority of the corrosion and then used a black boot polish to blacken the red rust colour a bit. The two core mains cable was replaced with some modern three core, fabric covered, braided flex from Savoy Hill

The intervalve transformer was open circuit. I enquired about the cost of a rewind but decided this set didn’t warrant such an expense. My solution was to replace it with a resistor and capacitor coupling. Again I must thank the members who helped me. I didn’t want any replacement parts on show so I made a cardboard replica of the transformer and hid the parts inside it. The old transformer will be kept, should I or any future owner wishes to rewind it.

The metal rectifier was an unknown quantity, but visually it was, again, very rusty. The whole thing was dismantled and the metal parts de-rusted with oxalic acid and then painted. A threaded rod, insulated with a paxolin tube, bolts the, whole, lot together and I managed to ‘stuff’ this, 5mm diameter tube with a 2W 680R and 2W 330R, connected in series (to drop the voltage) and a 1N4007 to rectify. The threaded rod was cut up and the two ends were Araldited into the ends of the paxolin tube and everything was reassembled

The original smoothing capacitor was missing and had been replaced with a rectangular, cardboard. A request for information, resulted in, forum member Boom, posting a picture and measurements of the original part. The photo showed a familiar looking cylindrical capacitor, but the crimped, sealed, end was at the top at the opposite end to the terminals. I found an identically sized Hunts cap, emptied its contents and with the aid of a mystery mains socket, a bottle top and a little picture of the manufactures logo (that I made from Booms photo) I was able to make reasonably good likeness.

The Bakelite, lozenge shaped, TCC capacitors were fine, as were (much to my surprise) the oblong, metal cased, multi-section capacitor… although it needed repainting.

There were two, black, waxed paper 1500VDC capacitors, connected in series, across the mains, at the base of the mains transformer. I managed to disconnect them, while leaving them in place and I replaced their functionality with a, single, 0.047uf class X2, hidden from sight. I replaced two more identical capacitors under the chassis. It was easier to make replica capacitors covers, on the computer, rather than re-stuff the originals, so that’s what I did.

The reaction and volume capacitors had a lot of muck and corrosion on them and following another help request forum member PJL suggested Viakal bathroom cleaner as a possible cleaner. I’m happy to say it worked a treat. The Tuning capacitor was boiled briefly in washing powder and then all variable capacitors were rinsed, dried and re-lubricated.

The 500K grid bias resistor was open circuit. I was a long grey thing, with a similar appearance to a fuse. I had nothing that looked like it so I chopped a bit the end and grafted in a 470K Eire resistor. Some grey paint, helped to hide the bodge.

The other type of resistor, in this radio, were smaller and are covered with a Systoflex tube. This made disguising modern replacements very easy.

Speaker
The voice coil was rusted to the magnet pole. Stripping it down, de-rusting and painting resolved the problem. The output transformer had an open circuit primary but once I removed the secondary, I was very pleased to find and fix the in the break. The original dust bag was used as a template to fashion a new one.

Baffle board
The baffle board had warped, and de-laminated but I managed to glue all the parts back together and clamp it all up. The bits that were missing were filled with car body filler. To finish a piece of Sid Chaplin speaker cloth was used

Back cover
Tony Thompson (Aerodyne) posted some very detailed measurements, in response to another one of my appeals for help. With these I was able to make a new back out of 3mm MDF. Another forum member, chipp1968, very kindly sent me an identification and licence plate, which finished the job off nicely

Cabinet

Luckily, the cabinet was in good condition and only needed a gentle wash and then polish up with brown boot polish.

That’s about it! It works well and looks considerably better than it did. Please have a look at the, attached ,photos

Regards
David
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Old 24th Aug 2010, 4:02 pm   #2
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Default Re: 1931 Ekco M23

....and here's a few more pictures, before and after, of the chassis

David
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Old 24th Aug 2010, 4:22 pm   #3
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Default Re: 1931 Ekco M23

Wow that looks nice! Well done

These sets perform well and are fast increasing in value.

My set is actually an RS2 which looks identical but is slightly earlier and uses a moving iron loudpseaker.
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Old 24th Aug 2010, 4:33 pm   #4
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Default Re: 1931 Ekco M23

I'm ashamed to admit I would have binned a set in that condition but you have shown whats possible !! Big well done, I'm officially amazed !
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Old 24th Aug 2010, 4:44 pm   #5
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Default Re: 1931 Ekco M23

Beautiful job, David. You went a step further than me when you stripped the chassis into bits. The only ones I've ever seen were cadmium plated, not painted - including the RS2's also. I spray-painted my M23 restoration but I left the chassis metalwork in one piece, obviously too lazy to do what you did!
Those intervalve transformers are a weak link. I've come across several that have gone o/c.
A lot of work, but well worth while. An amazing transformation.
-Tony
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Old 24th Aug 2010, 4:59 pm   #6
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Default Re: 1931 Ekco M23

Hi Tony,

I think the main reason I dismantled the chassis was because it didn't fit into the 3 gallon bucket of oxalic acid, while it was in one piece.

I should, also, admit that the resistor/capacitor coupling has compromised the volume a bit.

I may as well post some more pictures. The first one is a 'montage' showing how the intervalve transformer was made and the second shows how the rectifier was re-stuffed

David
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Old 24th Aug 2010, 5:34 pm   #7
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Default Re: 1931 Ekco M23

Splendid job, I do like the hole in the back so you can see the valves. "I should, also, admit that the resistor/capacitor coupling has compromised the volume a bit." shouldn't matter transmitters are so much more powerful these days, by a factor of at least 10.
 
Old 24th Aug 2010, 6:10 pm   #8
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Default Re: 1931 Ekco M23

That's taken a lot of effort! Well done!

Personally I prefer the rusty look but can't help but admire the sheer patience and skill you've put into this set. Well done
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Old 24th Aug 2010, 6:12 pm   #9
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Default Re: 1931 Ekco M23

That is an amazing job David, you must be very pleased.

Ian
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Old 24th Aug 2010, 6:16 pm   #10
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Default Re: 1931 Ekco M23

Quote:
Originally Posted by JoshWard View Post
Personally I prefer the rusty look
... Only a Morris Marina owner would say something like that
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Old 24th Aug 2010, 6:27 pm   #11
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Default Re: 1931 Ekco M23

it's called the 'distressed' look
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Old 24th Aug 2010, 7:24 pm   #12
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Default Re: 1931 Ekco M23

It's the engineer that gets distressed, not the radio.

Lovely repair job - well done.

Cheers,

Steve P.
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Old 24th Aug 2010, 8:02 pm   #13
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Default Re: 1931 Ekco M23

I would probably have done what threeseven suggested myself (slung it in to the bin) but what a result . it certainly puts my efforts to shame. cheers neil.
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Old 24th Aug 2010, 9:41 pm   #14
brianc
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Default Re: 1931 Ekco M23

A really fantastic job. One of the best "as new" restorations I've seen. Congratulations on a really excellent bit of work.
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Old 24th Aug 2010, 10:11 pm   #15
Phil G4SPZ
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Default Re: 1931 Ekco M23

Dave, that's a fantastic piece of craftsmanship and a nice readable write-up too. Well done.
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Old 24th Aug 2010, 10:26 pm   #16
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Default Re: 1931 Ekco M23

Fantastic effort!
I have a few sets in that state, i am now inspired to restore rather than rob them for parts.
Love the repro back, very well done

Mark
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Old 24th Aug 2010, 10:51 pm   #17
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Default Re: 1931 Ekco M23

Excellent write-up - and restoration!
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Old 25th Aug 2010, 8:34 am   #18
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Default Re: 1931 Ekco M23

Yes, quite inspirational to see what can be done with a lot of hard work and attention to detail. I'm amazed how simple the wiring looks on these very old sets. The '20s ones in particular look like they were designed as teaching aids rather than commodities. I was particularly interested in the resistor repair. I have been wondering about making replica "dog bone" resistors by encasing new ones in epoxy resin and painting. I suppose in some cases if they have just gone high you can wire up a suitable new one in parallel and hide it behind the original. It may even be possible to cut a groove in the carbon with a router and hide the new resistor in there then posision it in the chassis so the groove is hidden.
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Old 25th Aug 2010, 9:29 am   #19
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Default Re: 1931 Ekco M23

Brilliant job. That transformer rewind quote must have been an arm and a leg to not justify going ahead after such a fantastic job.
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Old 25th Aug 2010, 10:24 am   #20
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Default Re: 1931 Ekco M23

Thanks for all the positive comments

Quote:
Originally Posted by fidobsa View Post
I'm amazed how simple the wiring looks on these very old sets.
It's interesting you say that. I've attached a photo of the chassis, while it was in pieces and you'll notice how few passive components there are! It looks more mechanical than electrical

David
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