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Old 16th Jun 2019, 9:05 am   #1
sobell1980
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Default Ekco U49 restoration

Hi all,
After having a good run on my last repair, a Bush DAC90A I thought I'd get the next set straight on the bench. So the next set is the Ekco U49. Its a huge bakelite set with presets. The wiring on the chassis is a bit of a birds nest and access to change caps doesn't look as easy as when they are nicely rowed up as in the DAC90A. I think this set will prove more of a challenge.
I did some cold checks, checked the set over visually and put a temporary new mains flex on. I changed 'that' cap and went for a very brief power up with a 1 amp fuse. I know this set has it's own fuses but you can't be too careful . I was met with mains hum that would blow your socks off. I went on to do the valve checks, switching the set off between each measurement. The valve readings can be seen in the photo of my notes I made. But in a nut shell all the HT is well below what it should be. I also noticed the valve heater ballast resistor was on the wrong tapping so the valves were being overun being connected to 240 mains. I have corrected this and the valves are all now running on approx 18.50 volts ac.
The reservoir and smoothing caps are quoted at 8 uF and 24 uF. To get a dual electrolytic cap now with these values isn't possible. Looking up the CY31 valve data this valve can have a maximum reservoir cap of 32uF. Could I get away with fitting a dual cap of 32uF+32uF? Would I need to change the value of V5 surge limiting resistor to suit the change of cap? I've also ordered some X rated caps that sit across the line to suppress any line interference. Hopefully getting the reservoir and smoothing caps and some of the other large electrolytic replaced will help raise the HT ?
Well that's where I am so far.
Many thanks.
Dave
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Old 16th Jun 2019, 9:20 am   #2
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Default Re: Ekco U49 restoration

This is a nice looking set, being an AC/DC version of the A23
It would seem form the low HT/loud hum as if C53 has expired. probably C54 as well.
The good news is the output txf is obviously OK this has a feedback winding so is difficult to replace. It also show L24 is good ( choke smoothing - Posh ! ) 32 + 32 should be OK if 32 is shown as max reservoir cap. value. I can't see any reason to change the surge limiter, R37.
If you're keeping it original, C58/9 should be replaced with Y class caps. But that implies an external earth connection, so may be best removed ?
This shouldn't take too much to get up and running. You've change C47,most importantly.
Most of the other 'waxes' will likely need replacing, best done one at a time.

Andy
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Old 16th Jun 2019, 9:22 am   #3
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Default Re: Ekco U49 restoration

It may be safer to stuff the old smoothing/reservoir capacitor with the correct values or as near as you can get, say 10/22 mfd. The specification of the rectifier is 32mfd max but the valves are old, perhaps fragile, no point stressing the rectifier.
The surge limiter will require increasing if you decide to fit a 32/32mfd cap.

Edit. Oh well two different views on the problem.
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Old 16th Jun 2019, 9:23 am   #4
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Default Re: Ekco U49 restoration

The 32uF reservoir capacitor should be all right but increasing the series resistance can compensate for the increased capacitance.
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Old 16th Jun 2019, 9:29 am   #5
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Default Re: Ekco U49 restoration

Yes, I agree Trevor. Just wanted to run it by the experts. I was think about 125 ohms with a 32 uF cap.
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Old 16th Jun 2019, 9:37 am   #6
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Default Re: Ekco U49 restoration

Thanks for the reply Andy. Great advice there. Can I confirm what diagram you are using? I'm reading off trader sheet 827 for the U49. Some of the cap, resistor references don't correspond.
Dave.
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Old 16th Jun 2019, 11:17 am   #7
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Default Re: Ekco U49 restoration

If you use 10uF for the reservoir and 22uF or 33uF for the filter there would be no need to change the value of the surge limiter.

But if you do want to change the value of the surge limiter for an increased reservoir capacitance take into account that total Rs will include the resistance of the scale lamps/shunt.

Lawrence.
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Old 16th Jun 2019, 11:57 am   #8
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Default Re: Ekco U49 restoration

Quote:
Originally Posted by sobell1980 View Post
Thanks for the reply Andy. Great advice there. Can I confirm what diagram you are using? I'm reading off trader sheet 827 for the U49. Some of the cap, resistor references don't correspond.
Dave.
sorry for confusion Dave - I was working off the EKCO manufacturer's sheet as I can't seem to find the trader sheet on my disk. You'd probably be fine with a 16 + 16 electrolytic as there's a choke included in the smoothing circuit as well. Bear in mind that electrolytic values can be as much as +/- 50 % ! A.
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Old 16th Jun 2019, 1:39 pm   #9
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Default Re: Ekco U49 restoration

The reason I mention 32 uF and increasing the limiting resistor is from the valve data sheet. It recommends 32 uF with a 125 ohm resistor. Please see picture below. It doesn't mention as Lawrence interestingly mentions including the scale lamps and shunt resistance! I would have totally overlooked that part.

Dave.
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Old 16th Jun 2019, 4:35 pm   #10
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Default Re: Ekco U49 restoration

I would go for 10 and 22 and no other mod
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Old 16th Jun 2019, 4:43 pm   #11
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Default Re: Ekco U49 restoration

Hi Kevin I was hoping to go for a dual can type rather than smaller individual electrolytic caps. What are your suspicions for not modified it?
Dave
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Old 7th Jul 2019, 9:13 am   #12
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Default Re: Ekco U49 restoration

I managed to get the smoothing and reservoir caps sorted and got the HT up a little bit more and now have some sort of service. Lots more work to do yet but progress is progress! See the link to you tube.
https://youtu.be/Qg76ZNVhtQk

Work continues to recap the set carefully. Got some crumbling insulated wires to replace.
Many thanks
Dave
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Old 28th Oct 2019, 9:35 pm   #13
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Default Re: Ekco U49 restoration

Evening all,
Progress has been slow on this set but managed a few hours over the weekend. I've done a few more caps and some wiring where the insulation has crumbled. I have stations now on MW and LW amongst high pitch whistles and birdies! I noticed the IF cores had all been moved and a slight tweak of these brought in Radio 4 loud and clear and silenced the whistling. So that will need checking correctly with the sig gen.

Scale lamp bulbs! These were lit at a normal level. Every now and again they would pulse for a split second bright white. Eventually this happened longer and both bulbs blew in front of me. The bulbs I used were 12v 2.2 watt. I measured my voltage on the two wires supplying each end of the bulb chain. I was met with 44 volts! If I measure across the bulb shunt resistor I get the same reading. If I measure at fuse 2 on the neutral side of mains to chassis I get the same 44 volt reading. I've not replaced all the caps or decoupling caps yet but thought I'd post my findings on here. Appreciate any replies. The mains plug is fused at 1 amp.
Many thanks
Dave.
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Old 29th Oct 2019, 6:10 am   #14
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Default Re: Ekco U49 restoration

I forgot to say, that's 44 volts ac between neutral mains / fuse 2 and chassis.
Dave.
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Old 29th Oct 2019, 2:00 pm   #15
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Default Re: Ekco U49 restoration

I expect the pilot bulbs have blown due to the suppression caps being leaky, cut them out before doing any more work on the set, it will still work even f you don't replace them, possibly with more interference. I would regard the fuse in the mains neutral as a hazzard, assuming the set is correctly wired with chassis at, or near mains neutral, if the neatral fuse blows, or the set is switched on without it fitted, the chassis will become live through the heater chain. I've always thought the a23/u49 are fab looking sets, I've repaired quite a few a23s, got a u49 at the NVCF this year that is still awiating attention

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Old 29th Oct 2019, 4:45 pm   #16
sobell1980
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Default Re: Ekco U49 restoration

C43 and C44 suppression caps have been replaced with the correct safety x rated type. So unless the new ones are faulty it may be something else. I can easily snip them out and see if they are faulty though.
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Old 29th Oct 2019, 5:02 pm   #17
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Default Re: Ekco U49 restoration

If they are new they are probably ok, maybe you have a heater/ cathode short, or a short somewhere else
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Old 29th Oct 2019, 5:39 pm   #18
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Default Re: Ekco U49 restoration

My guess would be a heater cathode intermittent flash over in one of the valves. Study the circuit to indicate the most likely culprit.
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Old 29th Oct 2019, 9:44 pm   #19
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Default Re: Ekco U49 restoration

I've just tried removing each valve in turn working from the last in the heater chain to the first. I had the same result for each valve. 1.5 volts ac with a valve removed and 44 volts ac with the valve fitted. The same reading on all 5 valves.
It was then I noticed whilst switching on and off the set that with the set OFF I have approx 20 volts ac from neutral to chassis. That is obviously taking the measurement before the on, off switch at the fuse.
Dave.
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Old 29th Oct 2019, 9:46 pm   #20
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Default Re: Ekco U49 restoration

So essentially the set is disconnected from the mains and I've got 20 volts ac from neutral to chassis!!!
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