Replica Ekco A22T (A22 export model)

[Yorkie]

Coming on really well now Robert!

Thanks for posting the update, including so many pics.

Many are attracted to the circular Ekcos simply because of their external appearance, but it's only when you see one 'undressed' that the elegantly designed well thought out electro-mechanical features can be appreciated. The tagstrips around the outside periphery of the chassis make for ease of servicing and restoration. The tuning 'wand' which lights up just that portion of the dial to which the set is tuned and the 'backlash' slow motion tuning which allows you to rapidly tune the dial to a portion of the band, then turn slowly back to tune in stations are nice features. I've found the standard A22 excellent on the short-wave band, so I'm sure that your A22 Export Model will gave a very good account of itself.

[Radio Fixer]

Coming on well Robert. When I completely strip a chassis, apart from doing a diagram and marking wires with small circles of coloured H/S tubing (better than labels as they dont fall off or get in the way) I also check each wire to the circuit diagram. Sometimes differences will be found, either made in manufacture or afterwards by a service person. Of course you then have to decide which is correct, the chassis or the circuit.

I have made replica resistors and remember taking a lot of care and running tests to see that the resistors used inside the tubing were not overheating. Their W rating of course would be in free air. I mention this with regard to the idea of putting small resistors inside the ceramic tubes of the Erie resistors. Personally, I wouldnt bother to do this and like the 3W metal film types bought from Farnell which are about the right size and not too bad in appearance to resistors of the period.

Gary

[pwdrive]

The resistors I used from Farnell, the .7 watt ones are good to 100 + degrees centigrade, obviously you would not want them to run that hot if in a ceramic tube, I did a whole chassis with these and the 1 watt ones (they are even smaller) however the 2 watt ones are just a tiny to large to fit in those Erie ceramic tubes. I generally only do any restuffing if the set is of some note, otherwise it's straight replacement with the modern ones, I have yet to try to put modern resistors in the old dog bone body tip dot types, it should be feasable though.

Lawrence.

[Radio Fixer]

I havnt looked it up but I would have though the wattage decreases with ambient temperature ... instinct tells me? They arent .7 W at 100 deg are they?

Gary

[pwdrive]

Hello Gary, I am not sure what the exact parameters are for those particular resistors but I have given some of them a good frying in the past (by accident) and they seemed to hold up ok, but just to reitterate I would not advise in general running resistors hot unless they are wirewound and suitably rated, when I selected mine to go into the ceramic tube bodies I checked their circuit positions and functions to ensure they did not run hot, most of them were high value types used as agc/grid leak resistors and small signal anode load and screen resistors. I will have a go at doing a couple of body tip dot ones at some point but I will need to find some high value donors for one method.

Lawrence.

[Robert Darwent]

I halted the completion of this thread due to the project appearing as an article in an upcoming issue of the BVWS Bulletin. Since that issue has recently been sent out, and the 'cat is out of the bag' as it were, I am pleased to continue the project here too for the benefit of non-BVWS members.

Chassis restoration

Continuing, I renewed all the wiring between the major components mounted on the circular chassis and the tag-board;

   

and then fully rebuilt the chassis;

               

Fortunately, the original screening braid which carries the wiring between the tag-board and volume control was in good condition and could be reused, it was just a case of carefully threading the new wiring along its hollow centre.

Regarding a replacement for the missing loudspeaker. I was fortunate to already have a 6.5 inch diameter, 3 ohm speaker amongst my previously mentioned spares. Although not from an A22, it originally came from a related Ekco model, it was exactly the type required.

The bronze speaker ring was more problematical. I didn't have one and a number of possible solutions were contemplated during the course of the several months this project took to complete. None proved really satisfactory, then quite unexpectedly an original bronze A22 ring was listed and purchased via eBay. The final missing piece of the jigsaw had been found!

Modifying the mains transformer

A standard A22 has three tapping points on its mains transformer to select different voltage ranges, the A22T being an export set has an additional three. The body and size of the two types of transformer are identical, the A22T just has a much larger voltage selector panel fitted.

Obviously I couldn't replicate the additional three lower voltage tappings, but I could replicate the appearance by making an appropriate reproduction A22T voltage selector fascia and fitting the existing A22 selector panel to its rear.

This would involve extending the existing wires between the transformer winding and the selector panel and rotating the selector itself from the horizontal and refitting vertically in the centre of the new fascia.

The reproduction voltage selector consisted of two parts, the existing paxolin panel which the tap selector was attached to and a graphic of the A22T selector fascia, printed and laminated several times to achieve an appropriate thickness, fitted in front.

The 'U' shaped metal bracket that forms the front of the transformer, mounting the selector panel with two rivets, had to be fitted the opposite way around in order to provide the clearance required from the transformer windings.

The rivets were carefully released using a modellers drill and a burr tool. This enabled them to be reused to secure the new selector panel. Observant readers will note that they have been refitted a little lower and should actually be in-line with the middle voltage taps. This was a necessary compromise due to the 'U' bracket used being approximately a quarter of an inch shorter in height than the one used in an original A22T.

           

Although not necessary in terms of making the set work, I felt the cosmetic modifications worthwhile. The voltage selector panel along with the dial are the only two things that visually differentiate the A22T from the A22, so I thought it important to try and reproduce them both for the sake of authenticity.

Initial testing

The time had finally arrived to switch the set on! After double-checking everything I connected a temporary aerial and applied power via a lamp limiter with the set switched to the medium wave range. No indications of anything amiss from the lamp and twenty seconds or so later I'd got a definite background hiss from the loudspeaker. Switching out the limiter and tuning around brought in several stations loud and clear.

I'd expected this of course, or rather hoped. The cores of the medium wave coils and the two IF transformers had been untouched, so providing my component and wiring renewal was carried out correctly the set should have worked on this band. But what of the two 'new' short wave ranges.

Trying the S2 range first produced little until I reached the 10 o'clock position on the dial, when suddenly a foreign language station came booming out of the loudspeaker! Further careful tuning found several fainter stations as well. Switching to the S1 range produced very similar results. Clearly both ranges were working, which was something of a success in itself. Whether they were in the correct band of frequencies was unclear at this point, but I was very encouraged by what had already been achieved.

Alignment

Adopting the alignment procedure outlined by Ekco in their service data for the A22 as a guide, I began with the I.F. alignment. Using a signal generator coupled to the grid (top cap) of V1 (ECH35) via a 0.1 uF capacitor, I injected a modulated signal at 465 kHz. As instructed, the set was switched to the medium wave range and the tuning capacitor was fully meshed.

I don't have an audio output meter, so the adjustments were simply gauged by ear. Working backwards from the second I.F. transformer, cores L17, L16, L9 and L8 in that order, were each peaked for maximum audio output. As expected, the I.F. alignment was pretty much perfect already and no significant adjustments needed to be made.

Next came the I.F. filter consisting of L1 and C1. Injecting a 465 kHz into the aerial socket, the core of L1 was adjusted for minimum audio output. Again the alignment was close to ideal already, as L1 had also not been disturbed.

Then the adjustments for calibrating the three tuning ranges. To begin with, the physical position of the dial needs adjusting so that when the tuning capacitor is fully meshed the shadow of the pointer on the illuminated tuning arm coincides with the calibration spot just under 'M' on the lower right of the dial. I had already ensured this was the case when fitting the dial earlier.

   

S1 range (8.5-23.0 MHz) - Dial tuned to and signal injected at 22.0 MHz, adjustment of oscillator trimmer TC4, followed by aerial trimmer TC1 - Dial tuned to and signal injected at 9.0 MHz, adjustment of the core of oscillator coil L10/11, followed by the core of aerial coil L2/3.

S2 range (3.0-8.5 MHz) - Dial tuned to and signal injected at 8.0 MHz, adjustment of oscillator trimmer TC5, followed by aerial trimmer TC2 - Dial tuned to and signal injected at 3.5 MHz, adjustment of the core of oscillator coil L12/13, followed by the core of aerial coil L4/5.

MW range (550-1550 kHz) - Dial tuned to and signal injected at 1500 kHz, adjustment of oscillator trimmer TC6, followed by aerial trimmer TC3 - Dial tuned to and signal injected at 600 kHz, adjustment of the core of oscillator coil L14/15, followed by the core of aerial coil L6/7.

All the adjustments were made for maximum audio output and repeated until no further discernible improvements could be made. The medium wave range needed little adjustment because it had not been disturbed, and surprisingly the two short wave ranges were close to their optimum settings as well.

I attributed this to the fact that I had carefully adjusted the coil inductances and trimmer capacitances as accurately as I could with a digital LC meter during the rebuilding of the coil-pack board, setting them to their calculated values.

Using the signal generator to inject various frequencies on both short wave ranges confirmed that they were accurately operating within the required band of frequencies. Tracking was as good as I had hoped for, with all frequency points matching the dial markings to within a couple of widths of the tuning pointer shadow.

Regards

[Robert Darwent]

And images of the completed replica;

                   

This project pushed me further than any other restoration I had previously undertaken. I broke into new ground in terms of calculating/making the coils and rebuilding the coil-pack for this set, something I hadn't even contemplated attempting before.

All in all, I am very pleased with how the project turned out. The end result has more than surpassed the initial expectations I had when I started. It was well worth the many hours of hard work.

Regards

[Robert Darwent]

For the benefit of non-BVWS members, attached is the pdf of the project in article form as it appeared in the BVWS Bulletin magazine (Vol.37 No.3 - Autumn 2012).

Regards

[Aerodyne]

Skill, craftsmanship and meticulous attention to detail are the essentials requirements for the success of projects as involved as this one. Your abilities speak for themselves with this impressive work, Robert. Superb quality.
Thanks for sharing this with us.
Tony

[Mark Hennessy]

Simply wonderful - thank you for sharing this with us. Makes my restorations seem a bit basic, but thanks for giving us all something to aspire to

Mark