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Old 28th Jan 2022, 3:36 pm   #21
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Default Re: Ekco A22 repair started at last.

Quote:
Originally Posted by Herald1360 View Post
The 6B8G is interesting as an EBL31 sub. If you can live with maybe 1W audio output (plenty for domestic radio listening, most early trannies and valve portables managed with around 200mW) then it could get a set back on air for rather less than the real thing. It would probably fit in the sets where the crudely rebased EBL1s won't as well.
You may need to add a series resistor and decoupling capacitor in the screen grid feed to the '6B8G' valve, as the maximum quoted screen grid voltage is 125V. Whereas 'EBL31' screen grid voltage can be up to a maximum of 250V.
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Old 29th Jan 2022, 10:37 am   #22
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Default Re: Ekco A22 repair started at last.

Yes, mister valve, thanks. I did see that in the Brimar manual. Previous repairer/ owner just plugged it in! He was a bit of an enthusiast. Only thing different was a 250uF instead of 25uF cathode capacitor. I still use it with the 6b8g whilst working on it, just in case of an accident whilst on the bench. I did find my EBL31 and it tests excellent. That is reserved for when all work is complete.
I must say, volume is quite reasonable as is. I will measure what output power the 2 valves each give some time and post here. If anyone doesn't want to pay out for the EBL31 and can accept a lower (but quite adequate) volume, the 6B8G is a good alternative, with reduced screen voltage for safety.

On another note, the SW oscillator is now working. I used a gdo to verify the resonant frequency of the oscillator coil whilst fault finding and found it invaluable in eliminating suspect parts of the circuit.
I also made notes of the resistance of each coil and rf o/p in the oscillator.
I will post these notes here at a later stage, when I have completed alignment, just in case I can add any more information I gained.

I must say, just how poor the image rejection is on SW, just have to take care aligning. To be expected really. For many years I have been used to more professional receivers!
In the end, I just use my counter to verify what freq the osc is on.

I had a problem with the tuning gang and intermittent shorts approaching full mesh. I used my 500v megger and the arcing gave a good visual indication! It also eventually burnt away any debris left after cleaning with ipa and a blast of air.

I must say I find it strange posting about my own repair of a vintage radio, I normally read others. Apart from R1155, RA17 etc, it is many decades since I repaired a valve domestic set.
I am finding it quite interesting and absorbing.

Rob
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Old 29th Jan 2022, 12:01 pm   #23
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Default Re: Ekco A22 repair started at last.

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Originally Posted by robinshack View Post
I must say, just how poor the image rejection is on SW, just have to take care aligning. To be expected really. For many years I have been used to more professional receivers!
In the end, I just use my counter to verify what freq the osc is on.

Rob
Indeed. Nearly all domestic radios with SW have poor image rejection above about 10 MHz. During alignment I tune the LO in onto a nearby radio with digital readout, so if an alignment point is say 15.000 MHz/20m that's where I put the vintage set's dial. Then tune the digital radio to LO+IF (say 15.465 MHz) and move the vintage set's oscillator trimmer until I can hear it on the digital radio, and then carry out the usual trimmer/inductor each-end calibration. Using a nearby radio removes the possibility of the counter pulling the LO if there is a direct connection.

That's the LO set. Then set the calibration oscillator to 15.000 MHz which should now appear on the vintage set and complete aerial/mixer alignments.

I expect many of us do this, but it's a good trick for anyone not familiar with the nearby-radio technique.

Incidentally, I have a couple of A22s and when properly aligned and with a good set of valves they have a noise-limited sensitivity of about 2 to 4uV on a 30% mod signal on all bands. That's perfectly respectable for a domestic set, although academic as local interference is going to be way higher than that!

Ian
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Old 4th Feb 2022, 7:39 pm   #24
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Default Re: Ekco A22 repair started at last.

Thanks Ian. Yes, this one is very sensitive as well. Really impressed.

Starting final run of re-assembly now. I have taken some pictures at various stages which I will post probably tomorrow.
The loudspeaker cloth was damaged and talking with my wife, we went into town looking for material. We found a ladies blouse in a charity shop for £2.75. By Next, if anyone interested!
After cutting out a piece carefully and ensuring to centre the repeating pattern, this has fitted very nicely and I am very pleased with the result.

My current problem is on the perspex dial, with scratches on the back which show through when illuminated. I have tried various painting attempts. OK if one or two isolated marks, they will cover if I mix up a very similar colour paint. But no use for one particular area with lots of scratches. Pictures attached.
Trying to repair this damage will not succeed by just painting it all over, as the different thicknesses of paint will still show up the scratches. I tried it!

Has anyone any ideas to rectify this please?
I wonder if anyone has removed the entire reverse side paint covering and re-sprayed the entire surface?

Thanks,
Rob
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Old 4th Feb 2022, 8:05 pm   #25
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Default Re: Ekco A22 repair started at last.

Just for info's sake there's presently excellent repro dials on eBay.
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Old 4th Feb 2022, 9:11 pm   #26
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Default Re: Ekco A22 repair started at last.

Hi Rob,

Your A22 is coming along nicely! The new speaker cloth looks good too. When reviving my one I also had trouble with shorting in the tuning gang, probably not helped by it having lived in a swamp for some of it's life, and I also used a Megger to see where the short was occurring! As for your dial problem, I'd be tempted to leave well alone, make sure the felt pads are present on the tuning pointer shadow box, and that they are clean to avoid making it any worse. I can vouch for the replacements available, as my own A22 needed one, the only thing I noticed about them was that they are a bit more flexible than the originals, which isn't a problem.

Pleased to hear that you are enjoying the restoration! If you fancy something to read, have a look at this A22 restoration! Which I have still yet to finish...

Regards,
Lloyd
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Old 5th Feb 2022, 11:37 am   #27
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Default Re: Ekco A22 repair started at last.

Quote:
Originally Posted by robinshack View Post
Thanks Ian. Yes, this one is very sensitive as well. Really impressed.

Starting final run of re-assembly now. I have taken some pictures at various stages which I will post probably tomorrow.
The loudspeaker cloth was damaged and talking with my wife, we went into town looking for material. We found a ladies blouse in a charity shop for £2.75. By Next, if anyone interested!
After cutting out a piece carefully and ensuring to centre the repeating pattern, this has fitted very nicely and I am very pleased with the result.

My current problem is on the perspex dial, with scratches on the back which show through when illuminated. I have tried various painting attempts. OK if one or two isolated marks, they will cover if I mix up a very similar colour paint. But no use for one particular area with lots of scratches. Pictures attached.
Trying to repair this damage will not succeed by just painting it all over, as the different thicknesses of paint will still show up the scratches. I tried it!

Has anyone any ideas to rectify this please?
I wonder if anyone has removed the entire reverse side paint covering and re-sprayed the entire surface?

Thanks,
Rob
Your speaker cloth looks good. I never thought of using cloth from actual clothes! I've found on this set that it's not easy getting any vertical pattern truly vertical by aligning with the top mounting screw hole on the 'piece symbol' thing. It's just a bit out and can't be twisted straight. I've got to live with it or re-mount it at a 'jaunty angle' and not attempt vertical alignment. I think Ekco did that, or chose patters that were more irregular.

Yes, new repro dials are available on eBay for the A22. I've bought three over recent years.

Ian
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Old 6th Feb 2022, 12:48 pm   #28
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Default Re: Ekco A22 repair started at last.

The volume control looks original, 1M, spst switch. Morganite. It measures around 1.3M total.
With volume at minimum setting, the audio sounds low, but not very low. With it removed from the set, it measures around 50k from wiper to earthy end at the just "on" position. However, dismantling it, it seems it was made like this, as the switch actuation takes up this lower end of the track. At "off", the wiper is at the end of the track. At just "on", it is around 1cm along the track.
Anyone else seen this happen?

A few more pictures. One is the volume pot.
Another is the replacement transformer it has had fitted before I got it. Looks the part!
Two are the cabinet front, before and after. It will get a final shoe polish when work is complete.
The last shows a before and after on part of the cabinet.

My method of cleaning the bakelite is this:
I first cleaned it with surgical spirit, then some generic brand mister sheen type spray was applied and used to clean up any remnants from the spirit. Finally the brown shoe polish, the type in a flat tin. This was left to dry maybe 20 minutes before polishing.
I am very pleased with the results.
For these procedures I use some cotton wool type pads that are stitched around the perimeter and covered in a thin type of cloth.
Used by my wife for makeup removal etc.
I buy my own now for the workshop, less than a pound for around 60 or so in a pack from Aldi.
They don't fall to bits easily and I throw them away when used.
Previously I used various off-cuts of rag. Problem was, they could be contaminated without me realising what their last use was and what they might contain.


Thanks all for the help and advice,
Rob
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Old 6th Feb 2022, 1:08 pm   #29
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Default Re: Ekco A22 repair started at last.

Quote:
Just for info's sake there's presently excellent repro dials on eBay.
They use the artwork I published here, for purists there is one deliberate mistake and one lettering "I couldn't be bothered to find the function in the software" small error.

The chap has done a good job though and I did offer it for anyone's use.
 
Old 7th Feb 2022, 10:43 am   #30
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Default Re: Ekco A22 repair started at last.

Thanks merlin, did see that before. I have done some more "touching up" of the dial scratches and it is acceptable to me. Btw, the light paint covering on the reverse is immediately on top of the dial lettering. I was very lucky that the scratches had not damaged any lettering or dial markings.

Regarding the minimum volume, I phoned a friend locally to ask if he had a suitable pot. He is going to have a look. However, he suggests that it may have been made deliberately like that so as a user was aware it was still switched on when turned down to minimum. A google found a similar opinion on another forum.
He also has a nos EBL31 for me, so I am pleased I rang him.
I have used stevehertz idea of a pencil lead and managed to reduce the lower end track resistance a little, as well as applying the lead throughout the track length.
Again, I am happy to leave it as it is.

Yesterday around 1600, I was hearing a few ssb stations on 40M & 20M band, as well as the 5.**Mhz volmet. I used my sig gen as a bfo. Stability on sw is amazing. Aerial used is approx 18ft length from my upstairs shack, out through the window and along a short length of gutter.
One slight problem after replacing into it's case is top end of MW is now 1430kKhz, so need to readjust alignment a little.
I also am now running the dial lamp at 5V via a resistor from the 6.3V.
I have left the 5Z4 metal in situ. Two reasons. First, a 5Z4G envelope is very tight against the mains transformer and doesn't insert exactly as it should due to fouling. It also gives about 40V more ht than the metal one, so more heat is generated. Besides, the metal one ht supply of 252V gives more than enough audio at maximum volume.
I will leave the radio on R4 whenever I am in my shack. I am happy it should now work without further problems.
I am going to experiment with a frame aerial and a ferrite rod aerial as well.
Next stop a pantry tx!
I will post some more pictures as well.
Rob
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Old 15th Feb 2022, 11:39 am   #31
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Default Re: Ekco A22 repair started at last.

All finished now and working extremely well. I must say, performance exceeded my expectations for such a straightforward circuit design.
The work was all done indoors on my very small bench area available, approx 18" x 11" clear surface, surrounded by soldering equipment, drawers and storage. My outside shed has about 3ft x 22" bench area free, but needs heating on this time of year to be comfortable.
I have found this project most interesting and satisfying. My aim was for good performance with reliability. Hence, some modern components within. I am keeping the 5Z4 metal rectifier in there as well.
It will be moving into our lounge when we get suitable furniture to place it on.
I have attached some pictures.

I also took some measurements that may be of use to others.

Audio output comparison between EBL31 and 6B8G.
Settings were MW, strong signal, 1000kHz (300M), modulated 1kHz @ 30%
EBL31 fitted, gave 5V p-p across loudspeaker. More than enough volume!
6B8G fitted gave 1V p-p across loudspeaker. Sufficient for our lounge.
Both are at start of visible distortion on my scope.

Serial number is 018904
Front end information:
Using trader service sheet circuit component numbers, I give my coil dc resistance measurements for each band, measured between C7 and C14/C35 junction.
LW, 16.1 ohms. MW, 13.1 ohms. SW, 10.3 ohms.

Local oscillator injection measured as dc at junction of R3/R4. I used a 22k resistor in series with my Fluke dvm, set to dc. A 22k was put in series to avoid rf loading caused by my meter and leads.
This was with a used ECH35 that tested as “good” on my tester.
I checked at LF, Mid, High frequency, and results are given below in that order.

LW. -2.3, -5.5, -5.9. M. -10.3, -13, -7.9. SW. -2.3, -5.2, -6. All dc volts.

Thanks to all for the input to this thread.

Rob
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Old 15th Feb 2022, 11:53 am   #32
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Default Re: Ekco A22 repair started at last.

A good, honest, high quality restoration with unashamed sensible use of modern components. Well done. And yes, they do perform surprisingly well especially on short waves!
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Old 15th Feb 2022, 11:57 am   #33
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Default Re: Ekco A22 repair started at last.

More pics....
These show the scratches to the dial and the original damaged speaker cloth. That cloth is retained behind the new one to add support.
With the dial illuminated in the area of most scratch damage, around 1500M LW it is not perfect, but acceptable to me. This can be seen in one of the pictures showing it lit up. This was achieved by mixing a fairly close colour using Humbrol model enamel paint, then touching in very carefully.
I used some thin plastic sheet as a palette and held it over the area I wanted to match. Sounds easy. However, I found this extremely difficult to mix from my palette to achieve the required colour. I did wonder at one stage about going to one of the larger diy stores and getting them to mix some and buying the test pot. Only £3 or £4 istr.

Pictures showing illuminated will be in the next post.

Rob
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Old 15th Feb 2022, 12:01 pm   #34
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Default Re: Ekco A22 repair started at last.

Illumination pictures.
Note my cluttered work area. It is mostly like this, I just have too much stuff!
It is nice and warm, a small bedroom and I am 3 feet from the radiator.
Rob
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Old 15th Feb 2022, 12:11 pm   #35
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Default Re: Ekco A22 repair started at last.

Great job on a fine set.

I've not seen the screened metal cap on the EBL31 before in this set, just the bakelite tab with resistor and felt pad.
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Old 15th Feb 2022, 12:17 pm   #36
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Default Re: Ekco A22 repair started at last.

Thanks Steve. I moved the mains input tag strip and fitted sleeving.
Ian, it is not original connector, but is practical. The grid stopper resistor is fitted inside it. If you look nearer the beginning of this thread you will see the 6B8G that was fitted when I got it, together with some wire soldered to where the top cap should have been.

Rob
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