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Old 7th Apr 2020, 5:35 pm   #1
ORAWA01
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Default Marconi C100 B28 vs. Eddystones

I am looking to buy another vintage boat anchor receiver. Which one is better in performance and ease of repair & maintenance?

C100 is the receiver I have been trying to get quite a while, and read about it. For the Eddystones, I saw a a few for sale, but I don't know much about them.

Which is better option for general SWL (AM, SSB and CW) and ease of repair = parts availability, space to work on in the chassis and technical challenges in understanding how the sets work etc.

I read the C100 often compared with the AR88 in performance, but Eddystones seems not getting mentioned in that comparison = does it mean they are in different league?

Thanks
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Old 7th Apr 2020, 6:10 pm   #2
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Default Re: Marconi C100 B28 vs. Eddystones

Eddystones can vary from the built-down-to-a-bargain-basement price to the largely-money-no-option; you need to be a bit more specific as to what model(s) you are considering.

If you're after serious CW/SSB listening you need a decent crystal-filter; the CR100 has one as standard but it's only a single-crystal, which gives a good 'slope' for CW listening but is less than ideal for SSB.

A 2-crystal filter gives a somewhat better slope for SSB.

The CR100 - and many cheaper Eddystones - lack a HT voltage-regulator for the VFO/BFO: again depending on your local mains-voltage stability this can mean SSB?CW operation is somewhat frustrating.

The CR100 has two tuned RF-stages - and with a 465KHz IF needs them to reduce image-interference above 10MHz. Some of the cheaper Eddystones have a 465KHz IF and only a single tuned RF-stage, meaning images can be a real problem (with such an IF the 14MHz amateur-band potentially has an image that tunes across the 15MHz shortwave-broadcast band...).

Some of the later, CW/SSB/amateur-oriented Eddystones use dual-conversion and a higher IF so can get away with only one RF-stage, followed by conversion to something like 85KHz where it's possible to get good selectivity.

Similarly, the CR100 and early/cheap Eddystones don't have a product-detector, which means CW/SSB reception is not so hot.

Many years ago I had a CR100, which I "hot-rodded" by replacing the first RF-amp with a 6BA6, and fitted a 150V purple-glow-tube as a voltage regulator. It still wasn't _that_ good.

I currently have an Eddystone 840A to which I've fitted a [Zener Diode] voltage-regulator for the LO/BFO, which does at least stop it shifting 500Hz when you adjust the RF gain control. Yes, it has image-issues above 10MHz, and no product-detector.

I lust after an Eddystone 888A.
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Old 7th Apr 2020, 8:02 pm   #3
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Default Re: Marconi C100 B28 vs. Eddystones

I suppose that when CR100 and AR88 come up in discussion, the Eddystone model that is nearest in architecture (though about a decade later) is the 680/730 series (single-conversion, 2x RF stages etc).

As mentioned, thermionic Eddystones range over a wide range of sophistication from AA5-in-a-sturdy-box 870 to spine-compressing 880 with similar topology to the Collins R-388 types.
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Old 7th Apr 2020, 9:07 pm   #4
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Default Re: Marconi C100 B28 vs. Eddystones

The image problem was solved in the dual-conversion Eddystone 750 of the early 1950s. See the original data sheet at
http://eddystoneusergroup.org.uk/Dat...PEC%201950.pdf
It was a general coverage version of the later 888 / 888A.

The article at
http://eddystoneusergroup.org.uk/Res...%20Article.pdf
details a full restoration of a 750, which is applicable to many other Eddystones (and other sets of that era). The end of the article also includes original information published when the 750 was first produced.

Or what about a nice HRO?

Best wishes
Peter G3PIJ
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Old 7th Apr 2020, 9:29 pm   #5
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Default Re: Marconi C100 B28 vs. Eddystones

I was lusting after HRO and AR88 at one time, but they were far too pricy for my budget at the time. Even now, I suspect they would be going for high prices? Not sure, I have not seen them for sale anywhere for a while. Or if they were for sale, they are usually far away for collection only basis. Another problem with AR88 was that they are just far too heavy. I am not sure exactly how heavy, but maybe in the region of 45kg? I am guessing. I had a R109 radio about 10 year ago, and that was 47kg. I really struggled lifting it even to move from one table to another. When I was working on the PSU inside, I felt like working on a car rather than radio. When I sold it to local buyer, there were 2 big guys came and lifted together, because 1 would not have lifted and walked into the car himself alone.

I thought CR100 would be a lot lighter than that, but someone told me that it is still heavy at about 37kg? That's a lot lighter than the R109.
I had an Eddystone briefly about 15 year ago, and I think it was a 670A. It was AM only model. It was fairly heavy but not too large, and very sensitive and dynamic receiver on SW. It had some connection problem on the wafer switch intermittently. I didn't keep it long and sold it on to buy something else.

But for other Eddystone models, I have no experience.

CR100 seems still going for good lower prices than other boat anchors, and if it is available for sale in local area via gumtree or eBay, then it would be possible to go and collect it for a lot less price than other receivers? Well, with this lock down situation, local collection might be tricky now, but when it is lifted and in normal times, it is more likely to be able to get them than other receivers?

The problem with this these vintage receivers is that with the age, they will all need repair or full restoration work to put to daily use, hence price should be taken this situation into account unless it is fully restored and fully working one?

So, I was also interested in knowing if CR100 would be easy to work on and restore and the parts are easy to get hold of with good price as well. And the same respect in Eddystones too.

For the SSB and CW performance, I have seen a few Youtube videos on CR100, and they sounded quite nice. And with many owners and users of CR100 still going strong, it would be possible to get some info and advice if repairing or restoring it?
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Old 7th Apr 2020, 9:50 pm   #6
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Default Re: Marconi C100 B28 vs. Eddystones

The CR100 isn't quite to the standard of the AR88. The AR88 has better sensitivity on the higher bands and has a voltage regulator for the oscillators. Back in the sixties, I saved up for about a year beyond when I could have afforded to get a CR100, and bought an AR88. So I really did put my money where my mouth is. 5 bob a week pocket money plus christmas and birthday presents plus odd jobs.

The AR88 is useable to receive SSB but hasn't the selectivity to handle close adjacent signals. On narrow BW it's very pleasant for CW. No product detector so the BFO deafens the AGC system and you must nurse the RF gain manually.

THe HRO is an equal of the AR88. Poor tuning resolution in MHz from those little graphs, but good resettability from that dial. It's maybe a little better than the AR88 at handling the presence of large signals. Same comments about SSB apply to HRO as AR88.

The Eddystone general coverage sets are fair, but not quite as well built mechanically as the AR88. Their much vaunted tuning reduction is fine, but a little wear in the plain brass bush of the tuning knob shaft allows it to rock a little and that produces a frequency shift equal to a fair amount of rotation. I've had to make new bushes for a few of these receivers. Again, they don't really have the selectivity/agc for SSB but can be made to work under favourable circumstances and with effort.

To do SSB on an Eddystone, Tanuki wants an 888A amateur bands only set. I have one of the later versions of it, the EA12. I think in a previous life this one served as the IF for the first moonbounce 70cm contacts out of Scotland. This has an 85kc IF and a notch. SSB reception is easy, performance is fairly good Selectivity is not as sharp as modern SSB radios. THey seem to be sought after, so prices are pretty high.

If considering valve boat anchors, then the Racal RA17 should be in contention. It's fine for AM, RTTY and CW. You can make it receive SSB and it's not too hard work, but add Racal's external SSB/ISB adaptor and it becomes rather good. Superb stability. Long and linear tuning scales (60 inches per MHz) I ran an RA117 for about ten years. That's a later version with a few improvements and a much better amount of audio power.

They've all got their individual charms and difficulties. They can all be fun.

I'd definitely avoid an AC/DC eddystone.

A lot of CR100 have been mucked about with in attempts at improvement. AR88 and HROs tended to get left as they were.

THe GEC is another pre-SSB set. Sounds nice audio, but an absolute pig to work on as components were built over components over components. Reliability spoiled by running too hot.

I've had a wide range of receivers over the years... the ones I've kept are:
AR88 (and one for spares)
Eddystone EA12
Racal RA1217 (Transistorised RA117 with SSB filters)
Racal RA1792 (built down to a cost, no preselector or RF filtering)
Icom R-9000 (30KHz to 2000MHz with spectrum CRT)
Icom IC-765 tranceiver
Icom IC-7700 transceiver.

Hope this gives you a bit of a feel for things.

EDIT: Update, RA117 weighs 67 pounds according to data plate on front.

David GM4ZNX
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Old 7th Apr 2020, 9:58 pm   #7
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Default Re: Marconi C100 B28 vs. Eddystones

Hi Pete.

A friend of mine had an HRO for sale many years ago that I quite fancied.
This was the rack mount 'full Monty' job with the speaker, power supply
and steel coil cupboard with a complete set of coils. And then I thought -
could I really face my missus with that lot, wasn't she just about reaching
her limit of tolerance anyway, so I thought better of it.

Favourite radios from the Eddystone stable were the 830/7 and the 680X.

Kind regards
Dave
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Old 7th Apr 2020, 10:26 pm   #8
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Default Re: Marconi C100 B28 vs. Eddystones

An interesting thread Old Radios. I think your location perhaps IS the problem. Apart from Eddystone, many sets are not that expensive currently. At one time R1155's [relatively light] were at a premium but that's now all faded! AR88's are actually 80lbs weight. [See my comments on today's thread in the TV section].

I do understand what you mean about lusting after radios! I often comment that these were so un-available to many of us that [strangely] nobody ever worried about the weight back then. What does that tell us The AR88 did struggle with a single IF stage but the build quality, apart from the self destruct Audio stage, was incredible for the time I had a DST100 once-cast iron, very rare and weighing 100lbs! The Tuning Dial was a Brake Drum or very similar. "Days Have Gone By" -John Fahey.

Dave W
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Old 7th Apr 2020, 10:32 pm   #9
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Default Re: Marconi C100 B28 vs. Eddystones

For valve single conversion jobs it's the HRO for me, easy to work on, simple elegant electronics, simple elegant tuning mechanism, had several over the years, all my comms receivers have now gone but if I was to have kept one it would have been the HRO.

Lawrence.
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Old 7th Apr 2020, 10:37 pm   #10
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Default Re: Marconi C100 B28 vs. Eddystones

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Originally Posted by dave walsh View Post
The AR88 did struggle with a single IF stage but the build quality, apart from the self destruct Audio stage, was incredible for the time
Uh? There are three 6SG7 IF amplifier stages (and two 6SG7 RF stages) in an AR88. I think you've got it crossed with something else.

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Old 7th Apr 2020, 11:27 pm   #11
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Default Re: Marconi C100 B28 vs. Eddystones

Maybe a confusion between single conversion and single stage?
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Old 7th Apr 2020, 11:41 pm   #12
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Default Re: Marconi C100 B28 vs. Eddystones

Yes, single conversion to the usual 455kHz IF strip is definitely a limitation, and one shared by a lot of sets. Having two RF stages to buffer a bunch of RF tuned circuits helps, but it's never very good. Double conversion was a big help.

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Old 7th Apr 2020, 11:46 pm   #13
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Default Re: Marconi C100 B28 vs. Eddystones

Not sure about this as you guys are much more knowledgeable but I always thought [and have read] that the single [standard] IF frequency design was compensated for by the overall quality of the set. Any failings can be explained by the rush into production for the war effort. A bit like now eh? They were certainly in widespread use both before and after the war! I've seen a price estimate at $2000 each. That's even more startling if they were just dropped down mine shafts as a part of the shady Lend/Lease deal I'm happy to be wrong. After all, we are still trying to find out what actually happened here and now with a virus, in 2020

Dave

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Old 8th Apr 2020, 12:11 am   #14
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Default Re: Marconi C100 B28 vs. Eddystones

I expect that cold commercial considerations had a lot to do with tales of post-war cruelty to AR88s- WW2 meant that the various theatres of war were awash with these sets. They were excellent performers and continued to have credibilty after the event, but RCA would have been keen to flog US government agencies and others shiny new and expensive radios rather than see any more AR88s continue in service than could be helped. It seems that UK forces liked them sufficiently to hang on to many, and even comprehensively refurbish some in the early '50s though.

They are indeed excellent sets- but it's kinda difficult to dodge the fact that they are big in every dimension and very heavy, so both accommodating them and working on them isn't the easiest.
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Old 8th Apr 2020, 8:24 am   #15
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Default Re: Marconi C100 B28 vs. Eddystones

Consider a mixer doing a down-converting job. It might be a mixer in a single conversion radio, converting the incoming RF down to an IF, or it could be converting one IF to a lower one in a multiple conversion receiver.

The task is to choose an IF.

If we make the IF low, then filtering becomes easier, we can make narrower filters if we wish, or we can make wider filters squarer and closer to ideal. Gain is easier to obtain. All these things are good. Bur the image at the input to this mixer is going to be separated from the wanted frequency by precisely twice the output frequency of the mixer. So while choosing a low output IF is great for those IF stages, it places a tougher demand on the filtering before the mixer needed to block signals on the image frequency.

In the case of a single conversion receiver, those input tuned circuits, blocking the image, have to be variable-tuned, tracking the receiver. You look at how much image rejection the spec demands, look at the sort of filters which can be made to work over the RF tuning range and pin the tail on the donkey. This tells you the minimum frequency the subsequent IF must be. Is that too high to make a fixed-frequency filter with the spec'd response needed by the modulation format you have to receive? if so, you need to have another converter to an even lower IF.

So you wind up with each down-conversion having limits placed on the ratio of input to output frequency set by the sorts of filters available/possible. At one time in the past we could make better mixers than crystal filters in terms of dynamic range and so the very highest performance receivers had to be done with all LC filtering, no crystals. I found myself working on hex-superhets! six conversions, lots of filters! and the measurement/demodulation was done at different IFs along the chain to suit different wanted bandwidths (down to 22Hz)

If you can use crystal filters, then their exceptional Q and stability allow very narrow bandwidths considering the centre frequencies they can do, so you can achieve a far higher ratio of frequency reduction per conversion in you receiver structure making lide a lot easier.

If you're tied to a single conversion like the designers of AR88, CR100, HRO, BRT400 and all those classic receivers were, then you have to accept compromises. Your IF isn't high enough for good image rejection, so you throw multiple RF stages at it and several RF tuned circuits with a multi-gang tuning capacitor. Your IF isn't low enough to do ideal filtering. You can do the width for an AM broadcast, you can get a bit narrower for comms AM, but your skirts are rather wide. You can drop in a single crystal to give a narrow peak for CW, but it's still relatively wide in the skirts. You don't get good shape factor. Multi-crystal good shape factor crystal filters do exist... they were developed in the twenties and thirties as channel filters for FDM multiplex telephone links - this is where SSB started, though nobody in telecomms imagined it could work over radio. But these filters were very expensive. Too expensive.

Besides, with a single superhet, you have to leave a gap in coverage around where you've planted your IF. And the bands you need to cover are somewhat planned around 455-465kHz. Marine radios started to use single conversion into high performance crystal block filters in 1.4 and 1.6MHz IFs. You can get these with well-shaped SSB and CW bandwidths. But you have to have somewhere you can afford to have your gap in coverage.

The next thing along was up-conversion. Plant a first IF above your tuning range and mix up into it. Use a crystal filter up there (30+ MHz) and make it narrow enough to allow you to mix straight down to a nice low IF. Another receiver I've worked on mixed 0-35MHz up to 50.015625MHz and mixed straight down to 15.625kHz. Those crystal filters were just a bit touchy!

Up-conversion allows you to fix your image problems with just a fixed lowpass filter which seems rather attractive, even accountants make happy gurgling noises.

But it later turned out that those RF tracking filters that did their best to fix images did another thing - they limited the total number of signals tenderising your mixers and amplifiers. It turns out that a good receiver still needs some amount of preselection to protect it.

So there you have it, a general run-through of the tangled compromises in planning the frequency conversions of a shortwave receiver.

They are all badly compromised, yet they all work - under suitable conditions. For each sort of receiver, you can concoct a set of circumstances where it will fail to deliver.

Perhaps the best way to choose one is not to look at what it can do, but to look at what it can't, and choose the compromise least damaging to your interests?

David
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Old 8th Apr 2020, 10:00 am   #16
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Default Re: Marconi C100 B28 vs. Eddystones

The Eddystone EA12 if in your price and you can find one,though I think there is one in the Eddystone Users Group at present for sale.

No,the R109 is not heavy and may be you got mixed up with the R107.
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Old 8th Apr 2020, 10:16 am   #17
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Default Re: Marconi C100 B28 vs. Eddystones

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Originally Posted by HamishBoxer View Post
The Eddystone EA12 if in your price and you can find one,though I think there is one in the Eddystone Users Group at present for sale.

No,the R109 is not heavy and may be you got mixed up with the R107.
Ahhh... thanks for correction.
My memories for that heavy military radio is fading the now part from it was massive and very very heavy.

The EA12 looks great. Will have a look. Thanks for your info.
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Old 8th Apr 2020, 10:20 am   #18
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Default Re: Marconi C100 B28 vs. Eddystones

Yes, that is good price for the EA12. I have already bought the CR100. It was £50, and the seller is going to drop it off, on the way to his family funeral.

If I paid for the courier, it would have been £25 - £30 or even more just for shipping, so I thought it is a good buy. And it comes with the original manual.
I am not so sure what state of the set is though.

But now next time when I want Eddystones, I know where to look plus local gumtree and ebay sales.
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Old 8th Apr 2020, 10:21 am   #19
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Default Re: Marconi C100 B28 vs. Eddystones

The EA12 is classed as one of the best for Eddystone. Mine cost me more a few years ago.
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Old 8th Apr 2020, 11:07 am   #20
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Default Re: Marconi C100 B28 vs. Eddystones

I would have loved an EA12 back then but they were definitely for "the few". A Rolls Royce item re appearance and price. It took me a long time to realise that the scales ran backwards though!

Thanks for that very clear analysis re making compromises to get the best IF David. I do recall a lot of emphasise on Dual [or even Triple] conversion designs in the sixties but that was out of reach in many ways. I think the G2DAF design in the RSGB Bulletin was very much admired, if not envied, by many of us lesser mortals and it even came out as a separate booklet eventually.

Being modular in construction, RF front ends of the Army R107 RX's were being sold off separately by one firm. I could afford that and I think I had some plan to buy one and link it to another set to get Dual C but they had all been sold by the time I raised the cash

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