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Old 25th Dec 2020, 1:49 am   #61
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Default Re: Marconi CR100 - £30 bargain

Merry Christmas everyone. I’ve ordered the caps I need, just waiting on them to arrive probably some time in the new year
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Old 25th Dec 2020, 2:43 am   #62
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Default Re: Marconi CR100 - £30 bargain

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Originally Posted by AmateurRepairer View Post
I’m missing the bottom bit with the prongs off the bottom of the can, is this easily remakeable
Yes it's easily remarkable, but what happened to it? Did you lose it, or was it missing when you got the set?

Are you sure some previous owner hasn't wired three new capacitors under the chassis and left the big one disconnected? That's a perfectly legitimate way of doing it.

This is why Uncle Bulgaria suggested taking plenty of photographs, and I will repeat that advice. Take them before and during the work. You may well have a photographic memory, but we will be in the dark when trying to give advice.
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Old 25th Dec 2020, 6:04 pm   #63
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Default Re: Marconi CR100 - £30 bargain

I'd need to see a photo to be sure what you mean.

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Old 25th Dec 2020, 8:01 pm   #64
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Default Re: Marconi CR100 - £30 bargain

This could be a record thread folks There's a few contradictions maybe going on AR. You seem to be working on various different tangents all at once and that's just between a few posts. You said you wanted to return the set to 1945 original condition and are aiming at a high standard [fair enough] but you put up two frontages to illustrate [post 20* and post 31*] which are different in themselves so I'm a bit confused!

The S Meter, for example, seems to be going all over the place! It didn't unoriginal in the square form but then you decided to maybe fill the hole [the no meter option] or maybe to seek out an 'original' round Meter and now you plan to use the round hole for a speaker ["Not one for the purists but I need a useful receiver" post 52*] I might be wrong but installing a spkr there, is one conversion that I've never seen before and definitely unoriginal as well.

I think you may need to sort out a firm plan re the look you do want to create before anything else at this stage AR. As carpenters say. "Measure twice and cut once!"

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Old 25th Dec 2020, 8:47 pm   #65
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Default Re: Marconi CR100 - £30 bargain

I appreciate what your saying Dave Walsh, I’m going to restore it back to ‘45 spec the best I can, I’m just playing round with ideas.
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Old 25th Dec 2020, 8:53 pm   #66
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Default Re: Marconi CR100 - £30 bargain

I’ve managed to get all the old insulation and muck out of the electrolytic capacitor can, can anyone suggest how do get the old aluminium out? Thanks
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Old 25th Dec 2020, 9:06 pm   #67
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Default Re: Marconi CR100 - £30 bargain

OK AR just read around a bit more or if you want to get on with something, follow the guidance to sort of get it working [as you seem to be doing] and worry about the presentation, authenticity and paintwork further down the line.

By the time it's running you will probably have other ideas. The meter is at least age authentic and you can, in fact, hook up an external speaker with no size constraints at all. These sets are not supposed to be that easy to work on so you might need to study that in the first instance. Don't assume that I'm that good on the technical side but one component at a time is a good rule I believe. You will get plenty of help but [again] small steps and follow advice. "The best you can" is a plan!

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Old 25th Dec 2020, 9:20 pm   #68
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Default Re: Marconi CR100 - £30 bargain

Please post a clear picture of the inside of the can.
Also, please post one of the power supply section under the chassis.
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Old 25th Dec 2020, 10:10 pm   #69
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Default Re: Marconi CR100 - £30 bargain

At least the ongoing discussion has highlighted one of the fundamental quandaries in the hobby- how far should "originality" go- AR says he wants a usable receiver and something like its 1945 state, IMHO that's not contradictory and the sort of thing that generally I aim for with vintage gear. In the '50s and '60s, there were mountains of surplus WW2 electronics around, the transistor semed to offer greater and greater promise, so everyone was trying to improve this commonplace old stuff with product detectors, fancy "improved" mixer stages, hot front end "toob swaps" and so on and so on. Some of it was sensible, some of it was half-baked, some of it was garbage, sometimes it was well-executed by ex-professionals, sometimes it was a dismal and dangerous mess by impetuous bodgers. Now with the passing of decades, the kit is rare, and rarer still in anything like original condition, plus there's a bit of re-discovery and appreciation of the classic pre-war books on wireless. That brings a realisation that the folk who designed these nigh-on 80 year-old sets actually had a pretty sound idea of what they were doing and that the end result was generally a successful and well-balanced compromise for its end-user.

I'd agree that the panel hole for the meter would be hard work to remedy, so a period-appropriate meter would be a good solution for the time being and there are various circuits possible for driving it- the simple IF cathode-current approach, or the more sophisticated unbalanced-bridge circuit. Think of the CR100 as a kit of metalwork, coil-pack and valves that is itching to have its potential revealed with decent, safe wiring and passive components- it's more or less a given that the various decoupling and PSU capacitors will need changing, the resistors are probably a less urgent task unless any are badly off-spec or charred/mechanically damaged. There probably aren't many common receivers in its class that cover such a wide swathe of spectrum, the dual-speed tuning drive is a delight when cleaned up and lubed and, as prviously mentioned, there's nothing horribly complex or mind-bending about it, just standard circuitry that is found in many domestic sets but in greater quantity.
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Old 26th Dec 2020, 12:12 am   #70
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Default Re: Marconi CR100 - £30 bargain

I think reading the thread again [TS] might demonstrate that AR appeared to be starting off with the highest ambition at first. It's only when he gets 50 posts in that he says he now "needs a useful receiver" but what sort? It's confusing either way! I was just saying forget meter/spkr or other issues just concentrate on what's there initially! Your advice to think of the CR100 as an extraordinary kit that can be developed into almost anything is absolutely spot on and we agree but I think the trick is for him not to be side tracked in different directions at this point. [Rambo seems to be still awaiting a response at p62* and P68*].

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Old 26th Dec 2020, 4:00 pm   #71
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Default Re: Marconi CR100 - £30 bargain

Hi.
I have a CR100. Its got no case unfortunately but was in reasonable condition otherwise.
It's got an "S" meter but unconnected.
The big mod though is the replacement of the two original RF amplifier valves KTW63 with a plate and EF95's. The sensitivity is very good but the tracking isn't wonderful. The set just sits and isn't used, I might give it away at some point.
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Old 26th Dec 2020, 4:09 pm   #72
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Default Re: Marconi CR100 - £30 bargain

Here are various pictures of the chassis. It would appear the guy before has tried to remove the valves and taken the tops off, and left the little copper wire exposed at the top, is this easily fixable or a replacement. I believe the can was made redundant as there appears to be a lot of electrolytics underneath here, also does anyone know if this peice of Perspex with circuitry on is original or is it an addition. Many thanks.
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Old 26th Dec 2020, 4:21 pm   #73
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Default Re: Marconi CR100 - £30 bargain

The perspex and the mounted pots look like an addition, maybe to do with the S meter mod. sensitivity? set zero?

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Old 26th Dec 2020, 4:54 pm   #74
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Default Re: Marconi CR100 - £30 bargain

I deffo think it’s a mod Lawerence, it’s going anyway as it looks out of place. Just lubricated all moving parts of all the mechanisms and luckily nothing too seized. Just waiting for my wages to kick in it to get some paint stripper for the front panel and some battleship grey spray paint.
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Old 26th Dec 2020, 4:57 pm   #75
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Default Re: Marconi CR100 - £30 bargain

Quote:
Originally Posted by AmateurRepairer View Post
I deffo think it’s a mod Lawerence, it’s going anyway as it looks out of place.
I would check it out with the schematic just in case something that was original was removed and it has to be replaced.

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Old 26th Dec 2020, 5:34 pm   #76
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Default Re: Marconi CR100 - £30 bargain

I had a CR100 as a student back in the 1970s. When I bought it it had already gained a S-meter, and the front-end valves had been replaced by EF85s an ECH81 and a 12AT7 rather-nicely-installed by way of precision-machined 1/8-inch silver-plated-brass plates; the modifier clearly had access to decent workshop facilities - and probably was 'in the trade' because the EF85s were branded Loyds (who were a TV-rental company back then).

At the time there was a period of good sunspots and everyone wanted optimal 28MHz reception - I guess thta was the motivation.

The horrid mustard-coloured-rubber-covered crumblewiring had also been replaced. Alas the ubiquitous leaky decoupling-capacitors hadn't been replaced, neither had 'that capacitor' coupling to the output-valve's grid. The resultant excess current-draw cost me the mains-transformer. Cue big rework-time. Mullard 'Mustards' were dirt-cheap back then because the audiophools hadn't cottoned-on to them. I fitted a mains-transformer from a radiogram and increased the cathode-resistor on the output-valve so it drew less current.

I also took-out the original smoothing-capacitor/valve HT-rectifier - fitting a pair of BY127 diodes and a purple glowbottle to provide a stabilised HT-rail for the LO and BFO, which made 'holding' transatlantic stations on 28MHz a lot easier.

These days such modifications would be viewed as heresy!

My CR100 had a cream-coloured front panel and the case was not-quite-Hammerite metallic green. It looked to me like this was original.
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Old 26th Dec 2020, 5:45 pm   #77
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Default Re: Marconi CR100 - £30 bargain

Yes I’m checking it now Lawrence, doesn’t appear it was ever fitted originally

Hopefully don’t need to do much to it, going to swap all capacitors and some of the wiring.
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Old 26th Dec 2020, 7:08 pm   #78
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Default Re: Marconi CR100 - £30 bargain

The CR100 wasn't intended to last. It was developed in the era where hostilities were starting to look inevitable, and they all hoped it would be over before Christmas...

So crumbly wiring, and use of whatever components you had around the place were the order of the day.

So keeping a CR100 or an R1155 going is somewhat harder than an HRO or AR88. The Americans of that day weren't expecting to be involved.

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Old 26th Dec 2020, 7:46 pm   #79
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Default Re: Marconi CR100 - £30 bargain

Thanks for the pictures, but if your camera doesn't have a flash, you need to provide some illumination somehow. I was hoping for an image like this

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So we could see what has happened to the main smoothing capacitor wiring etc.
The image is a detail from on on this site
http://www.philipstorr.id.au/radio/s...comms_rx11.htm

Here is another well documented restoration
http://www.chavfreezone.me.uk/2020/r...g-a-cr100.html
It shows the rebuilt smoothing capacitor very well.

With the pictures from those sites and others, you should be able to identify what is and is not original in your set.
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Old 26th Dec 2020, 8:36 pm   #80
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Default Re: Marconi CR100 - £30 bargain

I’ve done this soldering to a capacitor. Be kind I’ve never done any before lol. The wire was broken so I resoldeded the points and fixed the break, but can anyone suggest how I can prevent the rust setting in on the joint? Maybe electrical tape?
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