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Old 6th Mar 2021, 1:21 pm   #1
DonaldStott
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Default EKCO U122 - Restore or spares?

I've recently just opened up an Ekco U122 which, on first inspection, appeared to have been untouched. What I did resolve was the loud clunking that I heard when the set was moved and somewhat alarmingly the Output Transformer had been fixed to the front panel with two split pins, both corroded but now replaced with 4BA bolts, washers and nuts. The mains lead looked to be original twisted cloth but it is in fact three core with the earth wire cut off at both ends!

I opened the plug, sorted out the fraying wires and inserted a 3A fuse but when connecting my test leads to the L and N pins with the switch turned on I was getting 67ohms? Most troubling indeed was the on/off switch - there are 4 tags, two for the incoming L & N and two for the respective outgoing. Unfortunately with the switch either on or off I was getting continuity between any two pairs of tags you may wish to choose - even I knew that something wasn't quite right here!

Short detour to resolve the problems with the on/off switch:-

EKCO U122 - Faulty on/off switch

Meantime, I further disassembled the set and removed the aerial board to allow easier access to both sides of the chassis - some general pictures:-

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The Primary of the Output Transformer reads 839ohms (and the speaker crackles) while the Secondary reads 1.5ohms. The speaker itself measures 2.7ohms. Here is a picture of the confusing wiring (to me) associated with the Output Transformer and the Loudspeaker:-

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Other points of interest are the signs of overheating on R8 (Trader 995) and the 'strange' replacement for V5 (UY41):-

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In order to get this set to a stage when I can even consider a Live Test there appears to an inordinate amount of work to be done replacing components and crumbling wiring, notwithstanding a rusty chassis along with repairs to the case etc. Add to that two new bulbs, replacement knobs and a NOS UY41 - but that list could increase if I delve deeper!

So I haven't gone any further in case it's a non-starter although this set could be used for spares and repairs?
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Last edited by DonaldStott; 6th Mar 2021 at 1:27 pm.
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Old 6th Mar 2021, 1:27 pm   #2
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Default Re: EKCO U122 - Restore or spares?

The problems you've encountered so far don't seem at all unusual to me.

At the end of the day it's up to you to decide whether to repair it, restore it or use it for spares. We all have our own way of doing things. One point I'd make is that it's seldom an economic proposition to repair a set. You'll never get your money back, but we don't fix sets to make a profit do we?
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Old 6th Mar 2021, 1:31 pm   #3
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Default Re: EKCO U122 - Restore or spares?

It's certainly been in the wars. The first thing to do is work out what's happening with the dropper and rectifier.

If the case is good, you may be able to find a better U122 with a smashed case, and make one good set out of the two.
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Old 6th Mar 2021, 1:33 pm   #4
Simon Gittins
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Default Re: EKCO U122 - Restore or spares?

It seems a shame to scrap it at this stage.
A short cut with crumbling wiring is to sleeve it by cutting one end of each wire.
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Old 6th Mar 2021, 1:53 pm   #5
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Default Re: EKCO U122 - Restore or spares?

First thoughts suggest the the UY41 has been replaced with a silicon rectifier with a limiting resistor. The 'polo-mint' RS dropper sections have probably been used to replace the heater of the UY41 since they could be made to 'plug in' to the valve socket across the heater pins.

It's up to you what you do but I think it's perfectly restorable to original if its just a question of removing the polo-mints and silicon rectifier, rewiring the AC feed back to original and plugging in a new UY41. Then it should be the usual job of recapping and fault-finding as required. Not really all that much extra work.
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Old 6th Mar 2021, 2:07 pm   #6
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Default Re: EKCO U122 - Restore or spares?

Looks like a fairly normal/easy restoration to me. I wouldn't say that drop of wax is indicative of a problem with R6.

There's actually never that much worthwhile spares to be salvaged from an old radio, certainly nothing much that can't be brought new.

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Old 6th Mar 2021, 2:17 pm   #7
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Default Re: EKCO U122 - Restore or spares?

Quote:
Originally Posted by DonaldStott View Post

In order to get this set to a stage when I can even consider a Live Test there appears to an inordinate amount of work to be done replacing components and crumbling wiring, notwithstanding a rusty chassis along with repairs to the case etc. Add to that two new bulbs, replacement knobs and a NOS UY41 - but that list could increase if I delve deeper!
To me that's the challenge I enjoy, can I bring this back to life again? I’m always a little disappointed when I turn a set on and it just works. It if turns out to be a no-hoper I can remove any new parts anyway, and have some fun along the way. I didn't think the chassis was too bad.
Imagine the achievement when you get first sound.
But it’s your choice depends where you get your enjoyment.

John
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Old 6th Mar 2021, 2:48 pm   #8
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Default Re: EKCO U122 - Restore or spares?

The output transformer looks very similar to a Radiospares replacement if it is and it doesn't have a hum cancelling winding then something is likely to have been fudged, Radiospares did do a "choke" output transformer.

Lawrence.
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Old 6th Mar 2021, 5:12 pm   #9
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Default Re: EKCO U122 - Restore or spares?

Here is the top view of the Output Transformer with the Radiospares logo clearly visible:-

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The four Primaries are labelled 1. 2. 3. 4. while the five Secondaries are labelled F. A. B. C. F.

And the side view:-

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I love the text 'Instructions Enclosed'

So well spotted Lawrence - it's a Radiospares 'Standard Output Transformer'.
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Old 6th Mar 2021, 5:45 pm   #10
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Default Re: EKCO U122 - Restore or spares?

Quote:
Originally Posted by DonaldStott View Post
The four Primaries are labelled 1. 2. 3. 4. while the five Secondaries are labelled F. A. B. C. F.
Only the Secondary tags A and B are used and should give a Speech Coil Resistance of 2.5ohms.

The Secondary tags labelled F are "dummies", provided as anchoring points for field connections etc.

See here: -

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The F tags have been used for the two HT smoothing resistors which also appear to be be 'newer' replacements for R20 3.3kOhms.
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Old 6th Mar 2021, 8:31 pm   #11
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Default Re: EKCO U122 - Restore or spares?

It has certainly been got at, but nothing that can't be sorted out, I have restored worse!
What condition & colour is the case in?

Mark
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Old 6th Mar 2021, 9:07 pm   #12
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Default Re: EKCO U122 - Restore or spares?

Go on, give the poor thing a chance to live again! They don't make em anymore, and every one scrapped is another lost forever, OK, there's loads of them about now, there's 2 of them looking at me now! One green, one white. I revived one of them, it's not a bad set! They look pretty cool too... Basket cases are the most fun to work on, the worse the better! I'm currently working on an old 405 line Philips TV that was dumped in a loft for a very long time, damp and neglect have taken their toll, but it's slowly coming back, I'm just about to try adding a strip of veneer to the bottom edge of the cabinet, if that looks ok then I'll try french polishing it, The chassis is nearly functional too.

Good luck with the restoration!

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Old 7th Mar 2021, 11:56 am   #13
DonaldStott
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Default Re: EKCO U122 - Restore or spares?

Thanks for all the encouraging Posts - it was never likely that I was going to walk away from this challenge but I was just curious to know if there were any obvious showstoppers? Also interested to know of any known 'quirks' with the U122 that I need to look out for?

I've now satisfied myself that I understand the wiring around the Output Transformer and Loudspeaker, both working, and will move on to look at the silicon rectifier and dropper.

In Post #5 above, Sideband made it all sound too easy " ... it's perfectly restorable to original if its just a question of removing the polo-mints and silicon rectifier, rewiring the AC feed back to original and plugging in a new UY41." I need to take a step-by step approach to ensure that I understand what is being changed and why. For example, what is a polo-mint and why do they need to be removed?

I've never encountered a silicon rectifier of this type and can't make sense of the under-chassis pin arrangements, particularly the heater connections if I'm going to replace it with a NOS UY41? In Post #1 above I attached a photograph of the silicon rectifier and there are two (newish) blue wires running to the pins on the valve base - not sure what those are?

The dropper is cracked in a couple of locations and some of the insulation has dropped off - is this a problem? I'll check the resistance readings later but it's very grubby and needs cleaning before I get out the DMM!

As with most sets I've restored I've found it very useful just to spend time looking at the wiring and trying to understand the connections - especially comparing it with the circuit diagram. It's especially difficult with sets such as this which have been 'got at' in the past as you are trying to mentally undo what was in the mind of the 'Phantom Twiddler'!
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Old 7th Mar 2021, 12:13 pm   #14
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Default Re: EKCO U122 - Restore or spares?

If the UY41's valve holder is ok it's easy to revert back to UY41 rectification, just refer to the schematic, the substitute heater resistance should be removed and the silicon rectifier should be removed along with any additional surge limiter resistance that might have been fitted in conjunction with it.

Lawrence.
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Old 7th Mar 2021, 1:02 pm   #15
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Default Re: EKCO U122 - Restore or spares?

Quote:
Originally Posted by DonaldStott View Post
Here is the top view of the Output Transformer with the Radiospares logo clearly visible:-

Attachment 228429

The four Primaries are labelled 1. 2. 3. 4. while the five Secondaries are labelled F. A. B. C. F.

And the side view:-

Attachment 228432

I love the text 'Instructions Enclosed'

So well spotted Lawrence - it's a Radiospares 'Standard Output Transformer'.
I might be wrong but looking at the transformer and the data sheet photo's it looks like the primary hasn't been connected for optimum anode load impedance.....9k as opposed to 3k.

Lawrence.
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Old 7th Mar 2021, 1:49 pm   #16
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Default Re: EKCO U122 - Restore or spares?

Quote:
Originally Posted by ms660 View Post
I might be wrong but looking at the transformer and the data sheet photo's it looks like the primary hasn't been connected for optimum anode load impedance.....9k as opposed to 3k.
Thanks Lawrence - the Primary connections are on tags 1 and 3 which as you say is 9k and not 3k as per the data sheet. Strangely enough, tag 2 looks as if it had been used in the past?

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Which value is correct for optimum anode load impedance and why?


Meantime I'm focusing on the Dropper and have measured the values and traced the connections - shown in this diagram: -

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A bit intrigued by the 'flying' 150Ω resistor and BY127 diode in this picture: -

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Name:	U122 Dropper_1.jpg
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Old 7th Mar 2021, 2:24 pm   #17
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Default Re: EKCO U122 - Restore or spares?

Quote:
Originally Posted by DonaldStott View Post
Quote:
Originally Posted by ms660 View Post
I might be wrong but looking at the transformer and the data sheet photo's it looks like the primary hasn't been connected for optimum anode load impedance.....9k as opposed to 3k.
Thanks Lawrence - the Primary connections are on tags 1 and 3 which as you say is 9k and not 3k as per the data sheet. Strangely enough, tag 2 looks as if it had been used in the past?

Attachment 228525

Which value is correct for optimum anode load impedance and why?


Meantime I'm focusing on the Dropper and have measured the values and traced the connections - shown in this diagram: -

Attachment 228523

A bit intrigued by the 'flying' 150Ω resistor and BY127 diode in this picture: -

Attachment 228524
Basically optimum load is for best output in terms of power versus distortion, the valve data gives 3k as optimum and in the valve data the Ia Va plots show a 3k load line.

The 150 Ohm resistor is an extra limiter resistor that was fitted with the BY127 as I suggested earlier. It would have been fitted as a substitute for the UY41's internal resistance so as not to increase the HT due to the lower forward resistance of the BY127.

EDIT: Forgot to add that back in the trade in the old days I would have fitted a coil of wire between the limiter resistor and the anode of the silicon rectifier.

Lawrence.

Last edited by ms660; 7th Mar 2021 at 2:34 pm.
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Old 7th Mar 2021, 3:11 pm   #18
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Default Re: EKCO U122 - Restore or spares?

Quote:
Originally Posted by ms660 View Post
Basically optimum load is for best output in terms of power versus distortion, the valve data gives 3k as optimum and in the valve data the Ia Va plots show a 3k load line.
Understood, thanks. Tags 2 and 3 it is then.

Quote:
Originally Posted by ms660 View Post
The 150 Ohm resistor is an extra limiter resistor that was fitted with the BY127 as I suggested earlier. It would have been fitted as a substitute for the UY41's internal resistance so as not to increase the HT due to the lower forward resistance of the BY127.
So if I'm putting back a UY41 then I can do away with the 150Ω resistor and BY127 diode?
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Old 7th Mar 2021, 3:17 pm   #19
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Default Re: EKCO U122 - Restore or spares?

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So if I'm putting back a UY41 then I can do away with the 150Ω resistor and BY127 diode?
Yes.

Lawrence.
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Old 7th Mar 2021, 3:50 pm   #20
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Default Re: EKCO U122 - Restore or spares?

Quote:
what is a polo-mint and why do they need to be removed?
Those circular resistors in picture 3 of post 16 were intended as a cheap solution to one section of a dropper resistor having failed, they bear a slight resemblance to the mints with a hole in them.
The modification to replace the UY41 probably worked but there would be greater stress on the reservoir capacitor so it is better put back to original.
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