Ekco U243 restoration

[adibrook]

This is pretty much my 1st ''proper'' restoration project. So i thought i may as well document it here

Before i just plugged it in and replaced anythging that blew. But then again before old radios were usually considered by me as sources for components to experiment with valve amps.

This radio is different tho. I kind of like it. It is just a boring 50's run of the mill transformerless reciever, but it looks reasonable quality.

The speaker is big and the cab is also big, so i predict it will sound pretty good.

Also, i need a VHF radio for my shed to tune into the transmission of shuffled music from my laptop.

And finally i really want to restore the marconi thign i found properly, and restoring somethign else 1st will bring good experience.

So...i got it home and stripped it down. Took the shassis out of the case and took the case appart.

I seperated the tunign backround, speaker bulkhead and main case.

The man case has a little bit of woodworm. However today i treated it with woodworm killer. I really went over the top and soaked everythgin in it. Hope the little %$&*'s have a slow and painfull death.

The speaker bulkhead had no woodworm so i just painted it with one coat of floor varnish (really tough. I use it on guitars!) to protect it and soak into some of the parts where the woods softened with age, to make it more rigid.

The speaker itself is pretty good condition. No rips in the diaphragm and appart from flakign paint no problems.

The glass tunign backround has a crack and some paint flaking. However i think i can easily sort out the pain flaking. I have the perfect stuff...black nailvarnish. I use the really tough stuff (to protect nails when playign live) so it should hold well.

The shassis is pretty grubby. I got rid of all the dust with a paintbrush and hoover, and soaked all movign parts (like the tuning cap and all pots/switches) in WD40. I also put WD40 on bad rusty patches.

All valves have resistance across their heaters...which is good. I think i will build a small test circuit on my prototypign bord for the UL41. Feed it's heater from a variak, use my normal X63 amp-testing preamp and thesame components as the UL41 would be used with in the radio (but modern). If thers positive voltage on the grid than i guess thats bad news. The i'm putting in a UL84!

I got rid of the 0.1uf mains hum supression cap. It was realllly nasty. Hunts...and wax/paper. And it spewd it's wax all over the shassis. At least that protected that part of the shassis tho! I think i will replace it with a 0.47uf X2 rated cap off a scrap TV bord.

Also, as far as i know, it's good practice to connect the shassis to mains earth through a X rated cap of about thesame size. Is this right? (obviously it cant be connected to earth directly because it's live shassis). So i will fit a 3-core cable.

Also, i need to find THAT capacitor and replace it for a modern equivelant. (the ul41 grid cap).

[paulsherwin]

Don't fit a 3 core cable. 2 core is the correct type for this set.

The mains cap value isn't critical but 0.47uF is a bit high even so, and may stress the on/off switch. 0.047-0.1uF would be better. Old switch mode PSUs often contain suitable caps.

WD40, hmmm... You've done it now so you'll have to live with it, but WD40 is basically kerosene which forms a light oily surface cover. Unfortunately this attracts all sorts of crud and leads to future problems. You'll have to see what happens. You're not the first one to soak everything in it. It's good as a chassis cleaner since it dissolves grease, but it isn't recommended for pots or variable caps.

You can test the UL41 in circuit. Replace the grid coupling cap, then check the bias voltage on the grid with a DVM. It should be a few volts negative - if it's positive the valve is leaky. You can also measure the cathode resistor (don't rely on the marked value) and the voltage drop across it, and use this info to caclulate the combined anode and screen grid current. If the grid voltage and current consumption are more or less what they should be and the radio sounds OK, the valve is probably good.

Good luck, Paul

[adibrook]

DW40 is great for clearing off old crud. Once i'm finished with it i will soak everythgin in meths to get rid of the deposits WD40 left behind.

The 0.47uf cap was from a switch mode psu supply. I guess it was a tv and didnt have an on/off switch tho.

I have another one which is 0.1uf. It's not X rated, but it is rated up to 2.5KV.

I found a new Pgmy bulb at BnQ. It's thesame raiting but is smaller physically and matte rather than clear. Shoudl work ok tho.

Ok...as soon as the cap situation is resolved i think i'll power up the shassis.

[adibrook]

Ok,

I'v fired the set up with a 0.1uf X2 rated cap i found in a VCR someone dumped in my back alley.

The UL41 seems to magically be allright!

With the old 0.01uf grid cap it had like +12v on the grid. But then i replaced that with a modern 0.01uf ceramic disk cap, and now it works really well. The grid is not positive at all! My avo on it's lowest dc setting (2.5v) didnt move at all.

The radio works and picks up stations allright on every band exept LW. Maybe thats a lack of an ariel? Or maybe a o/c coil?

Also, the tunign indicator is like lit up full all the time. I'v never met this type of valve before. But it looks to be a directly heated triode type device, only with a flourescent anode.

Any idea why it would be at full all the time even when the radio is tuned off station?

[paulsherwin]

Good stuff Adi.

I think this set uses a ferrite rod for MW and LW. If so, it should work fine on LW without an external aerial. If it's dead check the wavechange switch contacts and check the ferrite rod coil for bad connections or an open circuit winding. Most of the electronics are the same for MW and LW.

The coil may also have moved on the rod. If there's any sign of this try moving it back to its original position. If it's way out reception will be very poor.

ISTR the DM70/71 shows a full bar with no signal, and the bar *shortens* when a signal is applied. You're right, it's a directly heated valve. As I said in another thread, it was originally designed for use in battery sets.

Best regards, Paul

[Dave Moll]

Originally Posted by paulsherwin

ISTR the DM70/71 shows a full bar with no signal, and the bar *shortens* when a signal is applied.

I have checked by powering up a set which uses one of these, and (to the extent that it changes at all) this does appear to be the way it works.

[Biggles]

In my experience DM70/71's don't seem to be very sensitive. I have a couple of sets with these in and they hardly change at all. If I remember correctly, the heater for the tuning indicator in this set may be fed from the cathode current of the output valve. Unusual. I think the DM70 may have been designed for battery sets.

Biggles

[adibrook]

Hmmm...pretty wierd.

The radio works perfectly now. I'm just waiting for the case to dry.

All works expet the tuning indicator. It's on no signal all the time.

I traced it's grid (orange wire) to a rotary switch. It's the inside rotery switch (thers two on thesame axle) and thers a 2.2M (?) resistor connecting the grid to another contact on the switch.

Various poking about (shorting the grid to various terminals that it shoudl be connected to when the switch is in cirtain positions, etc) did nothgin. Shorting the resistor didnt do much either...and pokign the switch contacts with a screwdriver to encourage them to make contact didnt do anythgin either.

The radio isnt bery loud either. That IS being played through a modern hifi speaker tho. However, i think the dreaded UL41 is actually fine!

There was a small RadioSpares ''midget'' choke that fitted where holes in the shassis suggested a bigger choke once lived.

Someone had tried to solder a terminal strip to the top of the choke. However, they made a RIIIIGT screwup of it. Doesnt anyone know that you cant solder to paint? Unfortunatly all the leads were allredy positioned for the terminal strip ebign ontop of the choke. So i took the choke appart, seperating it from it's metal brace, and soldered the strip to the brace properly, using flux and two soldering irons. It's pretty solid now.

The case has really come out well. The woodworm killer has dried now.

I absolutly soaked the bottom in floor varnish to soak into and fill all the worm holes. I also varnished the inside of the case. The wood is old and dry, and has some worm holes, so i thoguht varnish will soak into all the dry bits and make it more rigid.

I left the outside untreated, as i think it's suppsoed to be polished with bees wax.

[paulsherwin]

The tuning indicator should be connected to the AGC line, and will be switched depending on whether you're using VHF or not. It just shows voltages, and you should be able to measure some volts with a meter as you tune in a strong station.

The fact that the grid coupling cap was knackered suggests that the other caps will be in a poor state too. One of these decouples the AGC line so if it's leaky it will pull the AGC voltage down.

You should probably schedule half an hour or so to change all the caps valued 0.001uF and higher. Once this is done the radio will be in a known state and you'll be better placed to pursue real problems, if any. Often recapping results in a *huge* improvement in performance.

A modern hifi speaker is likely to be 8 ohms impedence. The radio is probably designed to drive a 3 ohm speaker so this will lose you some volume.

Good luck, Paul

[adibrook]

The case is nearly redy for reassembly.

I noticed that the radios case originally had metallised paper strips running around both sides of the case from the top. I presume these are a built-in FM ariel?

Anyway. They both got sucked up by the hoover when i de-dusted the set. But i stuck in new strips made of kitchen foil and varnished over then everywhere expet where they meet the copper contacts of the coil that connects between them.

I am kind of in the process of re-cappign now. Basically, replacing any cap i just happen to come across.

I have a Maplin ceramic caps kit, which is coming in really handy. Most caps i'v replaced so far seem to be Hunts 0.01uf's. One of them decoupled the indicators grid...but i changed it and no difference.

[adibrook]

UPDATE:

The case is back together and looks pretty good.

I'v replaced all caps i could find exept the rectangular flat caps (ceramic?). As far as i know they dont often fail. Please correct me if i'm wrong tho.

Pretty much everythgin seems to be decoupled by Hunts 0.01uf caps. It's annoying changing them for modern ceramics because theyre allways in the most awkward places.

So, i replaced all the caps...and now everythign works great exept the tuning indicator doesnt work. It doesnt light up at all!

I'll check for ht voltage on it's anode later...now i'm tired.

I'v tested the radio for a good 2-3 hours (i had the shassis playing through an 8ohm hifi speaker while i worked on the Marconi). Everythgin works great. It picked up several stations, but i just listened to the best quality one (even with a ferrite rod reception isnt too amazing, plus it's night time).

I remember one band (either LW of MW) being full of spanish stations, and other languages. I ended up listening to some station that had a program for bored people who cant sleep...they kept talkign about some evil conspiricy by some ex-argentinian police person to steal peoples babies...or soemthgin like that. It was MORE confusing than the insides of the Marconi!

Anyway, the radio held up allright. Everything got warm...but i guess thats normal in a crowded live shassis. The Ul41 seems fine.

So...now i need to find out whats wrong with the tunign indicator, and then put the shassis back into the case.

The shassis is pretty grubby, but i guess thers not much you can do. I got rid of all the dust and the WD40 deposits...so now i guess it'll allways be this colour (part rusty and part faded plating). Expet form one brand new patch, where the mains hum wax cap leaked wax everywhere which protected the metal.

[paulsherwin]

As people have said in other threads, these tuning indicators often don't do much even when 'working'.

If it's completely dead check the HT and heater supplies to it. You've probably disturbed something while recapping.

Try doing a simple AM RF realignment. This normally involves tuning in a weak station then peaking the output by sliding the appropriate coil along the ferrite rod. When you've found the peak, secure the coil with a bit of melted wax.

Best regards, Paul