3rd Oct 2022, 9:09 am | #21 |
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Re: Eddystone 840C
A few updates: Still not in a position to power it up but....circuit now returned to normal around the first I.F and the untidy tagstrip has been removed. The (I think) noise limiter mods re-introduced very badly has been removed and circuit returned to normal. There was a 3pF cap missing (BFO injection) so I've replaced that (I knew those very low value caps I rescued from Philips would come in handy sometime)! I'm awaiting some 0.047uF caps to arrive from Cricklewood Electronics since I've run out of them and this radio has lots of them so I can't replace the cracked Hunts until they arrive.
The fitted speaker left a lot to be desired. Once again very poorly repaired. The cone was rubbing badly against the magnet pole just by gentle finger pressure. Some tears in the cone had been repaired with (I think) something like EvoStik and again the wiring was atrocious. I'm not even sure it's the original speaker. It had rubber wires attached that were hard and crumbling and these had been joined to the original speaker wires by what looked like sticky plaster (Band Aid if any Americans are reading this)! So I decided that there was nothing to lose by having a look to see if it could be improved. The speaker came out easily enough and the two screws holding the magnet were removed. The coil itself was OK and now the the magnet and pole-piece had been removed, was free and the cone moved without restriction. The pole-piece was clean with no rust so it looked like it just wanted careful reassembling. I removed the centre felt from the cone and used a couple of paper shims to set the gap. The magnet and pole-piece was far easier to set up than I imagined and in five minutes or so, the two screws were tight, shims removed and I had a freely moving cone. Two more jobs to do....the cone was coming away from the frame....more than half was still attached so I ran some impact adhesive under the card surround and was able to make a neat job of gluing it back to the frame. Last job was to re-attach the centre felt dust cap. The speaker now worked OK (quickly tested by connecting it to a vintage radio). I removed the rotting rubber cables and attached new PVC wires. The speaker is now refitted and wired to the original speaker cables and the joins hidden by heatshrink......much neater than before. That's about as far as I can go until the new caps arrive. We're getting there!
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3rd Oct 2022, 9:43 am | #22 |
Nonode
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Re: Eddystone 840C
I have seen late new in box 840Cs for about £50, so they're worth restoring.
One final tip. On my 840C and 940 the outer case is almost an interference fit to the front, so when you fit the case insert a steel rule each side in the gap (say 2mm) prior to tightening the rear screws. This makes case removal easier next time. |
3rd Oct 2022, 12:32 pm | #23 |
Octode
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Re: Eddystone 840C
On the 840C I used to own the connections to the volume pot (wiper and top of track) were reversed ex factory! If volume adjustment seems a bit strange worth a look to check yours is OK.
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3rd Oct 2022, 3:22 pm | #24 |
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Re: Eddystone 840C
As an aside to that, I noticed yesterday that the date on the smoothing can was 1962. I'm surprised that Eddystone were still using B8A valves in 1962. I suppose they were cheap and still plentiful but were somewhat old hat by 1962 considering that B9A had been around for some years.
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3rd Oct 2022, 4:09 pm | #25 |
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Re: Eddystone 840C
I think Eddystone's QC must have been a bit hit&miss at times; on my 840A there was a joint in the band 1 local-oscillator part of the coilbox where the enamel hadn't been stripped from the winding and so it could _never_ have worked on that band!
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3rd Oct 2022, 4:16 pm | #26 | |
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Re: Eddystone 840C
Quote:
I don't remember B8A valves being used in the built-for-Military-service-in-the-1950s 730/4 receivers we had in the 60s/early-70s ArmyCadets/TA, I guess the MoD got the newer valves first!
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3rd Oct 2022, 9:50 pm | #27 |
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Re: Eddystone 840C
At least three of the valves could be original. I thought it would be worth running the valves through the Avo Twin Panel tester. Pleased to say there are no showstoppers (I don't have a single UAF42) and they all measure pretty well although I have replacements for all the others if necessary. The only one I couldn't check was the DM70 but I have a replacement for that if required.
Whoever fitted scale lamps used Blu Tac to secure them! I've removed them and cleaned all the sticky muck off. I suppose it's not a bad idea to fit scale lamps and if I decide to reinstate them with the small transformer I'll find some proper bulb holders. Caps next when they arrive and then some HT to see if we have any life anywhere.
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3rd Oct 2022, 10:53 pm | #28 | |
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Re: Eddystone 840C
Quote:
A quick search at least reveals the UAF42 to be one of the cheapest NOS valves there is- hopefully, it won't attract any aural mystique in the near future! |
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3rd Oct 2022, 10:57 pm | #29 |
Nonode
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Re: Eddystone 840C
A number of Eddystones from around this era, including my own 680X, need the tubular versions of the pilot bulbs to illuminate the dial properly. With the spherical versions fitted the filament sits too far back.
Al
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3rd Oct 2022, 11:53 pm | #30 |
Nonode
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Re: Eddystone 840C
If you can't find UAF42, surplus identical Marconi WD142s can sometimes be found.
Just tried my 840c and it still works, think I will do the dropper mod with internal slide switch to select R or C. For sets with no provision for filament lamps, I would tend to use white LEDs, only requiring 3V at around 10mA which might be available e.g. at audio o/p cathode. |
4th Oct 2022, 9:17 am | #31 |
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Re: Eddystone 840C
The odd thing is, whoever the previous owner was, he must have had a good idea of what was required. It just looked like he'd used a gas heated soldering iron and solder without flux...most of it just crumbled away. Lots of melted insulation which just makes everything look untidy and bodged. I have a nasty feeling that some of the alignment might have been tampered with as well. The beehive trimmers should be sealed with wax. Most are not and there are remnants of wax left on the spirals. The alignment doesn't worry me if it has to be done but I'm much happier aligning a set that hasn't obviously been got-at! At least the cores of the coils and I.F's are not damaged.
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4th Oct 2022, 8:53 pm | #32 |
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Re: Eddystone 840C
I suppose we've all encountered vintage items that have had slightly- or more than slightly- worrying bodges done to them through haste, penny-pinching, unawareness or just "this'll get it going just for now, I'll make a proper job of it.... sometime....". I worry slightly that one day a tragedy will occur from an incompetently repaired or modified second-hand electrical item that becomes high-profile enough to result in draconian legislation- ISTR that an MP's daughter was electrocuted in her kitchen as a result of deficient electrical work, resulting in far more stringent prohibition on what could legally be done on a DIY basis, despite the fact that the work in question had been done by a professional electrician. It's not too hard to envisage that private transactions involving second-hand electrical devices could end up being outlawed as a result of an instance of mishap through negligence/incompetence, already the screws are tightening from several different directions- the auction site paranoia exemplified by "spares or repair only", removal of mains plugs, the prohibition on removing items from industrial and council WEEE skips and so on.
Apolgies for deviating somewhat from "Eddystone 840C revitalising", but these metal-case, line-to-chassis sets are a prime example of something that would get a jaundiced view nowadays even in their un-kludged state and that sometimes have been prone to less-than-encouraging workmanship over decades of existence. A long time ago at work, a bundle of Siemens-brand trimmers were cleared out that I found ideally suited to the RF and IF cores in my 670A and 750 sets, the blade just the right size and made of a plastic that was neither too brittle or too soft for fragile cores with viscous coating- a deficiency of quite a few plastic trimmers. |
5th Oct 2022, 1:08 am | #33 | |
Hexode
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Re: Eddystone 840C
Quote:
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5th Oct 2022, 7:37 am | #34 |
Pentode
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Re: Eddystone 840C
Several other Eddystones also had "live chassis", as they were designed for AC/DC mains operation. The 840C was probably one of the last "domestic" AC/DC sets built bt Eddystone. One reason for for continuing to build AC/DC sets long after Britain had gone over to all AC mains, was the marine market. I sailed on several ships in the late 70s which still had 220vdc electrical supply.
Rod M0LXY |
5th Oct 2022, 8:46 am | #35 |
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Re: Eddystone 840C
Small update: All the capacitors I ordered from Cricklewood Electronics arrived so I made a start on the I.F and AF stages last night. Some of those .05uF caps are really buried under other components but I managed to replace all of them and the three electrolytics. Just in case there is anyone reading this who doesn't agree with wholesale changing of caps.....every single one removed was either O/C (in the case of the electrloytics) or so leaky they may as well have been resistors! The worst one was one of those nasty torpedo type capacitors that look like fat resistors....it read about 100K on the meter. It wouldn't have stopped the radio from working but the tuning indicator wouldn't have been doing much.....
Next I will fit the 2.5uF dropper cap. I would have done it last night but I need to enlarge the hole where the original dropper fitted....and my drill needed charging! I'm still pondering on how to replace the Hunts capacitors hidden under the coils in the front-end around the RF amp and mixer valves. There doesn't seem to be an easy way in and if they are anything like the ones already replaced in the I.F stages, they will be as leaky as sieves. Removing the extension rod to the wavechange switches might help. Once the dropper cap is fitted I might just get the HT up and see what happens....
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5th Oct 2022, 9:37 am | #36 |
Nonode
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Re: Eddystone 840C
A method I use in tricky situations is to make wire tunnels by tight winding a few turns of thin (0.3-0.4mm) TCW round a needle or thin drill. You can either butt the new leads onto the old and solder or if there is more room you can overlap the component leads.
This method still relies on there some access to the component but has got me out of a few jams. Al
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5th Oct 2022, 12:04 pm | #37 |
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Re: Eddystone 840C
Thanks Alistair. I was thinking of something along those lines. I wonder how Eddystone replaced them? They probably had the facilities to take the whole coil assembly out. I'm thinking of cutting the old cap out close to the leadout and then winding a spiral each end of the new cap as close the the leadout as possible and then slipping those over the old component leads. That might work.....
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5th Oct 2022, 12:56 pm | #38 |
Nonode
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Re: Eddystone 840C
I have also successfully used that method. The main problem with it is that it can be more difficult to make the loop on the component lead small enough in diameter. It all depends on the wire gauge.
Al
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5th Oct 2022, 1:03 pm | #39 |
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Re: Eddystone 840C
The other technique as used by Philips is to make small wire spirals (a few turns) and to slip the cut off end of the old component and the end of the new part into the spiral before soldering.
You can use offcuts of component leads, or something like 25gauge wire, to make the spirals.
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5th Oct 2022, 1:39 pm | #40 |
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Re: Eddystone 840C
Yes that's a neat way of doing it....if there is the space! I'll have to think more about the best way of doing it.
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