Eddystone S640

[Hermit6345]

Eddystone S640 Restoration Project.

Receiver was obtained in May 2011 the following observations were made.

.Bandspread system had been strung with baling string
Front LH speaker grille had two unsightly holes drilled through.
Die cast front panel was bent!
Mains transformer measured 3Mohm to chassis on mains winding
The BFO tuning knob was seized
The phones socket bezel was charred and half missing,
The RF gain knob above it looked as if it had been near an open flame and was bubbling and charred.
One dial lamp holder was MES and the other MBC
Aerial circuits on rear of chassis had been altered
Finger plate worn and scratched
Case paintwork scratched
Mixture of valves, some not even equivalents of the originals

It was decided, after reading Gerry O’Hara’s most informative and helpful articles on the EUG website, that nothing less than a re-cap, re-valve and replacement of all out of tolerance resistors would do. A couple of 35mm diameter 16 + 16uF electrolytics were obtained from the BVWS stock. The reservoir cap used just one section and the smoother used both in parallel.
The recap took quite a long time and it needed a steep learning curve to discover things like how the BFO components could be got at. The decouplers deep in the oscillator die cast box were a bit inaccessible for my rather large hands as well. As will been seen later, I missed one! A number of out of tolerance resistors were identified and changed. The AFPA sub-chassis was a particularly difficult unit to work on. I replaced a couple of wires with ones slightly longer than original to allow easier access to the underside.

In order to restring the Bandspread system the front panel had to be removed. It’s supposed to be possible to restring without removing the front panel, but I couldn’t see how! A couple of problems with the mounting arrangements on the Xtal ON/Offside switch and associated trimmer had to be overcome as did a seized knob on the BFO tuning capacitor.

Although it was possible to repair the unwanted holes in the front panel, the curvature in the die cast front panel was beyond my resources to straighten. I decided that a rough example of an S640 be obtained and used as a donor set. This would provide a new front panel, new knobs and a new phones jack bezel amongst other things.

It was at this point that I found local companies to strip/shot blast the front panel and cabinet of the donor set and also powder coat those parts in black with a finished texture similar to the original. Powder coating is a tough finish and thicker than spray-paint. A company was also found who could produce an exact copy of the finger plate. This was silk screened and anodised onto 0.8mm aluminium and was pretty indistinguishable from the original.

After doing all the replacement work, but before the front panel was replaced, the receiver was slowly brought up on the Variac. The HT rail was monitored and all was in order. Range 2 worked well but the other two ranges were very insensitive.. All of the LO trimmers and cores had been sealed at some time with some very hard sealant that finally succumbed to IPA. The BFO did not seem work and was found to be miles off its nominal 1.6 MHz. Poor sensitivity on ranges 1 and 3 was traced to a wire soldered to a tag on the wrong coil in the aerial input section. All ranges worked OK after the wire was moved to the correct position.

Once I got the front panel and finger plates back, I was able to start the re-assembly (After the restringing had taken place of course). It all went together reasonably well with knitting needles (as suggested by Gerry) used to hold the dial mounts in place whilst the screws were screwed in. Bit of a fiddly job that.

I then carried out a full IF and RF alignment.

I had seen a mod.to fit a small 3 inch speaker behind the LH speaker louvres so some 3 inch speakers were obtained from RS and fitted as per mod instructions. No holes required and speaker can be removed in a couple of minutes. Surprising fidelity from such a tiny unit.

The mains leakage was becoming a problem, tripping my Sig Gen and the final straw was when the transformer in my set began to hiss and gurgle. It was decided to bite the bullet and put the donor set mains transformer into my set. This one measured infinity between all windings and transformer case. I removed both the transformers. one from the donor set and the one in my set. Sean assisted with the soldering of the donor transformer in my set as my shakes were particularly bad that day and the wires are deep inside the PSU section. I fitted two fuse holders at the same time. One 100mA 20mm in the HT centre tap and a 1A 20mm in the mains line.
These were fitted to spare holes in the side wall of the chassis

Although I had replaced every waxie that I could see, a peculiar fault made me aware of the fact that I had missed one. After using the radio for some weeks, I switched on one morning and smoke was noticed but its source was difficult to identify. The HT was measured; it was low and varied with movement of the RF gain control! Breaking the RF gain control line into its feeds to the RF and both IF valves revealed that there was about 200 volts positive on the cathode of V1, the RF amplifier valve. On really close inspection, deep in the bottom of the RF amp die cast section was a carbon resistor which was showing signs of distress. Beneath it and hidden by the range switch, was a wax capacitor. The job of this cap is to decouple the V1 anode feed resistor. Its cold end is connected to the cathode of V1 and not to earth. This capacitor was dead short and was thus feeding full HT to the cathode of V1. The HT was then being fed along the RF gain control line to the cathodes of the two IF amp valves and to the RF gain pot. It was quite a job to get that little blighter out and because of recent serious eye problems I had to call in Sean to be my hands and eyes in replacing the capacitor and associated resistor Smoke now gone away and radio seemed to be none the worse for wear.

For a radio of this age (c. 1948) it runs well.. It resolves SSB beautifully in spite of it not having a product detector. It also seems to be meeting its original sensitivity and noise figures.

I am confident that it will now keep on going for another 65 years.

[HamishBoxer]

Great job on a classic Eddystone.Got one in my collection and must fire it up and see what state its in, though excellent cosmetically.

[newlite4]

Very nice job Ian and Sean. I am always impressed by these 'back from the brink' restos. Looks so much better for the new front panel assembly.
Neil

[Hybrid tellies]

Excellant job and great write up

[Neil Purling]

Back when I was a Short Wave listener I used to lust after an Eddystone receiver.
Is there a external speaker socket? That internal speaker surely won't do it justice.

[Radio Wrangler]

Eddystone routinely fitted quite decent internal speakers in their radios. My EA12 has a six inch driver and no cabinet rattles... and the sound is better than the SP-20 external speaker for my IC765.

David

[turretslug]

Excellent work, always good to see one of these classic radios refreshed and rejuvenated. Not just a "real" tuning gang but "real" bandspread to boot. Should be good for years ahead,

Colin.

[Hermit6345]

Thanks for all your kind words. It is nice to see them come to life. The components used in these sets seem to be quite high quality, although they suffer the usual problems with waxed paper caps.
As far as the internal speaker goes, there are a couple of terminals on the rear chassis apron and the internal speaker is fed from those.
Although the die-cast front panel has provision for two ~3 inch loudspeakers, they were never fitted by Eddystone AFAIK. It may have been something to do with purchase tax at the time. I have an original AR88 speaker and the radio sounds superb through that. I fitted an internal speaker simply out of a desire to operate the set without any external accessories. The little speaker sounds really good, which surprised me. Eddystone did make an external speaker for use with this range of sets but I have never been lucky enough to find one for sale. I have three Eddystone receivers now, the 640, a 504 and an 870. It's a pity that the 640 has string drives rather than a gearbox like the 504 etc, but it's very smooth for all that. The cabinet is back on the 640 so now it's totally finished.

[HamishBoxer]

Good Luck to you and look forward to your next restoration!

That case was just crying out loud for a 'speaker, there are some very good 3" units available these days. I popped one of these (a 4" unit, see pictures) into my EB35, it sounds marvelous.

[turretslug]

Nice work, Merlin. No way I can get one in my 750, though. Well, maybe on the underside of the lid but that would be butchery.

One of the external speakers mentioned was on eBay not so long ago- can't remember how much it went for, but rather more than many of the sets fetch!

[HamishBoxer]

Expect to pay around £80 depending on condition for an Eddystone speaker though more if it's in its original box.

[G6Tanuki]

Nicely done: a "sympathetic" restoration that's not compromised performance for the sake of cosmetics.

Must confrss, as a teenager I always lusted after an Eddystone EA12.

There is a school-of-thought which says these receivers really need to be listened-to using headphones to appreciate fully their design-engineering.

I say "It's yours - Listen to it however you want to".

--G6Tanuki.

[Phil G4SPZ]

Nice work, good to see another of these classic sets restored.