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Old 19th Oct 2014, 3:51 pm   #21
WaveyDipole
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Default Re: Eddystone 840A

David, thanks for the advice. I did, as it happens I did take picture. I don't think that the cleaning made much difference to the end result! Fortunately all markings on it are still quite clear and practically no flaking paint, but it does look its age.
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Old 19th Oct 2014, 4:23 pm   #22
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Default Re: Eddystone 840A

I'm slowly working through all of the capacitors that need replacing and having taken a queue from the excellent restoration advice on the Eddystone user Group, am currently taking the opportunity while the front pannel is removed, to replace the capacitors in the B.F.O. In the meantime, I am also pondering over a couple of other questions:

1. To reform the big can electrolitics or replace with modern equivalents under the chassis?

My first inclination, having replaced all the waxies and other paper caps that are likely to fail, was to wake it up gently to allow the big can electrolytics to reform. This would preserve originality. On the other hand, it might be easier/safer to go the whole hog and replace the electrolytics with modern parts located discretely under the chassis (which I believe could be accomodated)?

2. How to tidy up the front pannel and case.

The case is in the 'black crackle' finish. The front pannel looks clean but some paint has flaked off silghtly near the handles and along the bottom edge. The case is reasonable its age, being in reasonably good condition but looking a bit 'dusty' and having a few scuffs here and there, particularly on the edges. I have seen advice to use shoe polish and/or permanent marker to touch these in, but there is a fair bit to touch in. I also had the idea of painting in black hammerite, but this would ovbiously change the appearance. Any advice on the best approach here would be appreciated.

3. How to deal with the mains connector

The two pin connector is, of course, not compliant with modern standards. The previous owner had taken the trouble to mark it to identify which way around it should go. However, I do have a spare IEC 60320-1 C13 ("kettle" style) socket as used in PCs. I thought of removing the existing connector and replacing with the modern one (unfortunately there does not appear to be enough space to have both in situ). This would allow me to permanently wire the leads in the appropriate order and earth the case. Of course this would sacrifice some degree of originality, but in this case I think safety has to be a consideration?

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Old 19th Oct 2014, 7:13 pm   #23
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Default Re: Eddystone 840A

For the power-connection on mine I've fitted a 'captive' 3-core lead through a cable-gland. The lead is about a foot long and terminates in an IEC309 plug.

It mates with a RF line-filter in a diecast box - my modern rendition of the Eddystone "Cat 732 Mains Filter".
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Old 19th Oct 2014, 7:50 pm   #24
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Default Re: Eddystone 840A

Quote:
Originally Posted by WaveyDipole View Post

1. To reform the big can electrolitics or replace with modern equivalents under the chassis?

......

3. How to deal with the mains connector
There's always the "third method"

Restuff the cans...... best of both worlds that way.

Mains connector? I'd incline to keep it as standard. Paradoxically if you sold the set on, any modifications could cause more trouble than leaving it. Run it from an ISO TX or RCD protected circuit for your own use, if it worries you.
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Old 19th Oct 2014, 8:28 pm   #25
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Default Re: Eddystone 840A

While you've got the front panel stripped, there is one big weakness in the Eddystone standard tuning gearbox that is worth checking.

The tuning knob shaft drives a thin metal disc by means of a pair of sprung cone. This gives very smooth operation, no backlash, and a high ratio of reduction because of the small running diameter of the conical faces.

The downside is that a little angular play of the knob shaft through the bush in the panel is equivalent to quite a bit of angular rotation of the tuning knob, so wear in the bush quickly makes sloppy tuning.

It's not a complicated part so it would be easy to turn, but would need the right sized reamer to finish it.. 0.25 inch isn't an odd size. Maybe the EUG have these as a standard spare?

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Old 19th Oct 2014, 9:50 pm   #26
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Default Re: Eddystone 840A

I forgot to mention this earlier when Radio Wrangler suggested taking a picture of the tuning scale. If the scale is still out of the set can you also find and measure a couple of datum points on the scale, one horizontal and one vertical. It will help produce 100% accurate copies should they be needed.

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Old 20th Oct 2014, 10:12 pm   #27
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Default Re: Eddystone 840A

Alistair, the scale is still out of the radio so I took some measurements as you suggest and noted them on a sketch I made of the dial.

Herald, yes, there is also the option of stuffing the cans. Anyone know what the success rate for reforming is?

Incidentally, I did purchase that isolation TX that a member was selling. I think this is probably the safest way to go and means I don't have to modify anything. I can use the original plug and cable as well.

Radio Wrangler, that disc looks to be in reasonable condition. There is a little play on the shaft through the bush - its difficult to quantify. It probably won't move around much when the weight is back on it. The shaft isn't totally dry, but it does need lubricating. I might ask about this on the EUG forum as you suggest.

Anyone any thoughts on the paintwork?
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Old 20th Oct 2014, 10:35 pm   #28
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Default Re: Eddystone 840A

The discs seem to last and so do the shafts, all the badly worn ones I've come across have been due to bushes and if the bush lets you shift the knob without turning it, the tuning change can be quit a bit.

I re-did the cabinet and panel of a cabin receiver I'd bought back in the 70's, and I grit then bead blasted it. The casting went through the alochrome process, but as it was the wrong alloy it came out a disgusting runny grey colour, but it had made the aluminium paintable. I used a light grey sprayed hammerite and the result was very good indeed.

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Old 20th Oct 2014, 11:59 pm   #29
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Default Re: Eddystone 840A

Quote:
Originally Posted by WaveyDipole View Post
Anyone know what the success rate for reforming is?
Could well be good- whilst I extensively recapped my Eddystone 750, I left the 3 Hunts HT electrolytics (50, 50, 8uF) and dated 1950 in (once I'd done a leakage check). This set does have a low-value HT secondary fuse, though. I also built a power pack for another set (maritime, external power) using some salvaged Hunts elkos, more out of cussedness/curiosity- it's not as if modern replacements are expensive- and they've also given no trouble. I know "Hunts" is a dirty word in the paper capacitor world but anecdotally at least their electrolytics seem to be less of a disaster.

Naturally, if there's any doubt, don't, but the low HT in the 840A should also be a plus point.
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Old 21st Oct 2014, 12:07 pm   #30
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Arrow Re: Eddystone 840A

Quote:
Originally Posted by WaveyDipole View Post
How to deal with the mains connector.
The two pin connector is, of course, not compliant with modern standards. The previous owner had taken the trouble to mark it to identify which way around it should go. However, I do have a spare IEC 60320-1 C13 ("kettle" style) socket as used in PCs. I thought of removing the existing connector and replacing with the modern one (unfortunately there does not appear to be enough space to have both in situ). This would allow me to permanently wire the leads in the appropriate order and earth the case. Of course this would sacrifice some degree of originality, but in this case I think safety has to be a consideration?
Since you will be using this set with an isolation transformer, the case of the set (for electrical safety reasons) does not need to be connected to the incoming mains supply earth. (Obviously, earth the metalwork of the transformer and any case it's in). So you will have a pair of wires from that transformer to the set. Provided you have a 2-pin free socket to fit the fixed 2-pin plug at the radio, that solves your 'input power' problem.
Moreover, since that incoming 2-wire feed will be balanced to earth, it will not matter which way round the 2-pin connector is connected to the radio.
As for an 'earth' for the set to complete an aerial connection, there is an earth terminal available at the back of the set, I believe. (Naturally, that 'earth' is not directly connected to the case of the radio.)

Al.
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Old 21st Oct 2014, 8:06 pm   #31
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Default Re: Eddystone 840A

Yes, there is an antenna earth terminal at the back and in this case it is decoupled from radio earth (chassis) by a 10nf high voltage capacitor. I understand that antenna earth and mains earth are not the same thing.

Once I get the transformer I will have an idea of its size and will be able to find a suitable case. I haven't decided on metal or plastic at this stage, but if use a metal case I will be sure to earth it and include appropriate fuses. However, it was my intention to connect the radio to the transformer output by using the existing two pin plug only. I was considering connecting the case to mains earth earlier, before I chanced upon the transformer in the items offered section, but since the transformer does away with that neccessity, it means I can use the radio safely 'as is' without modifying anything which I think is the better option. I do appreciate the advice though as it would have put me straight in any event and it is re-assuring to know I am thinking along the right lines!
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Old 29th Oct 2014, 3:57 pm   #32
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Default Re: Eddystone 840A

While I have been waiting for the isolation transformer to arrive I've been getting on with a few other tasks. For example, I have painted the cover and front bezel. The bezel has a slightly satin look about it so I looked around for some black satin finish spray paint. I found Hammerite (£12) and Halfords satin black (£7.99). I ended up with the Halfords paint. I first tried a bit on the underside of the case. It actually looked quite good when dryed so I bit the bullet and carefully sprayed the whole case and the bezel with a fine layer. This came up pretty well, so I sprayed another 2 layers. The end product is actually quite good. I have attached a couple of pics. The second image is something I am experimenting with as regards adding a light.

The isolation transformer has arrived so I have something to test with once I have re-assembled the radio. I've started reassembly of the front pannel, but before I go any further, can someone advise me what to lubricate the two rails on which the pointer runs with? The pointer seems to run OK, but the rails are a bit tacky to the touch so I think they may be lubriacted with something. Should I leave them alone or shall I clean and re-lube?
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Old 29th Oct 2014, 5:41 pm   #33
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Default Re: Eddystone 840A

For the lubrication, what about one of these. http://www.greatart.co.uk/Pastels-Pe...ite-Block.html

Not sure what hardness would be the best.

Al
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Old 30th Oct 2014, 2:45 am   #34
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Default Re: Eddystone 840A

When I look at the schematic I get the impression that when a wander plug is pushed into the 'E' socket it connects the chassis to the Aerial earth.

The Aerial earth is isolated from the HT ground by a 0.01uF mica capacitor.

Even if used with an isolating transformer, the case/cabinet might get a bit 'tingly' when that 'E' plug is inserted.
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Old 30th Oct 2014, 5:13 pm   #35
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Default Re: Eddystone 840A

Silicon, it connects aerial earth to the case (marked CABINET) which is electrically isolated from the chassis. Nevertheless as you say, it is isolated from HT gound by a 0.01uF capacitor (C3). I have replaced this as it was a paper cap but I could have removed it altogether I suppose although I'm not sure how that would have affected the antenna. I would not have expected any 'tingle' unless there was an AC leak somewhere, but I will bear it in mind nonetheless.
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Old 3rd Nov 2014, 12:29 pm   #36
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Ok, I have re-assembled the front panel and re-attached it to the radio taking care to replace all the washers and spacers in the correct order. I checked that the case is still isolated from the chassis and so far, so good. The only slight problem is that the right hand side (looking from back) pulley is now leaning under tension into the pointer slider bar and the screw holding the pulley does not tighten. The pointer catches it and sticks. I slackened the line and unscrewed the pulley to find that one turn of thread on the screw is damaged. It probably unlikely that a replacement can be obtained and I'm not sure how to fix it at the moment. I also need to figure out how to line up the pointer back with the correct frequency on the display but this shouldn't be too difficult.

Other than that, the tuning mechanism works really smoothly and very well. I cleaned the the bars and re-lubricated them with white lithium grease. I also put a little on the cogs. Finally, I put a couple of drops of 3-in-1 oil into the little hole on the brass bush holds the tuning control shaft.

I've wired up the isolation transformer ready for testing which I will proceed to do once I've replaced the valves into the set. As regards a gentle waking up, I can see a couple of options. First there is the 40/60w bulb in series technique. But do I place this on the transformer primary or the secondary?

Then also it occurred to me that I could also start with the receiver power input set to 230v but feeding with the 110v supply? This can be followed by progressively going to 200v, then to 110v?

Also, how many hours do I allow on reduced power for capacitor reforming?

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Old 3rd Nov 2014, 1:17 pm   #37
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Default Re: Eddystone 840A

For capacitor reforming it might be better to pull all the valves and replace the rectifier with a 1N4007 in series with a suitable current limiting resistor. This will allow the process to start gently. Monitoring the voltage across the resistor will give an idea of the leakage current- remember to allow for any potential dividers which may be across the HT supply. When leakage current falls to a mA or three, reduce the resistor value and repeat the process. It'll soon be clear whether anything useful is happening.
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Old 3rd Nov 2014, 8:37 pm   #38
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Default Re: Eddystone 840A

Thanks herlad. I'm just giving that a go. I have a 4.7k 7W resistor in series with a 1N4004 diode (didn't have a 1N4007). When I first turned it on I was getting 46v across the resistor but its now been on about 20 mins and I'm now getting 48v which equates to just a little over 10mA. Not sure whether, perhaps, that is just a warming up effect? The resistor is quite warm to touch as might be expected. No funny smells or smoke, which is probably a good sign!
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Old 3rd Nov 2014, 9:29 pm   #39
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Default Re: Eddystone 840A

If the set hasn't had power applied for a long time, the HT electrolytics may have gone quite leaky and take a while to come good- give it till the end of the evening and see if there's significant progress. It's occurred to me that there's a UCH42 triode-hexode in the set- unlike heptodes, hexodes generally have their screen-grid voltage pretty firmly fixed by a potential divider (to discourage their inner tetrode from getting into mischief under AGC action) and this may look like a constant leakage, so allow for this, or disconnect one end if you can be inclined and can get to it simply. Also, it's likely that the first AF amp will have an HT feed filter of a few tens of kilohms and a few microfarads- if this latter is kaput in the sense of well leaky or short, it may look like a leakage that doesn't get better.
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Old 4th Nov 2014, 1:21 pm   #40
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Default Re: Eddystone 840A

I expect that it had been stored for some time. The owner's family member to whom the radio got handed down apparently powered it up after taking it out of storage and just got a hiss from it. I haven't powered it up fully yet.

I left it on all night and this morning we were back down to around 46.5v. There is, indeed, a potential divider on the UCH42 which I did miss. It uses a 22k and a 47k resistor in series, giving a total of 69k. At 47v this would draw around 0.7mA which means that I am still seeing about 9.3mA of current being drawn. However the slight voltage drop suggests that we may now be heading in the right direction. I will run it again tonight to see what happens.

The cap on the first AF amp, if I have the right one, is fed by a 22k ohm resistor and is a 50uF large can elecrolytic. It is identical to the two power soothing caps so presumably it should also reform? I can't see anything else obvious that would account for the current drain. I have replaced the waxies, although there are still 4 oil filled metal can paper caps mounted on to the chasis by a nut at one end which have not been replaced. I'm told these are generally OK?
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