Eddystone Model 850/2

[thoyer454]

I have a chance to buy an Eddystone 850/2. Not much on the web about them - rare I suppose?

There is one on the auction site for $5k dollars - is that what they go for? If so I may have to keep my couple hundred dollar offer to myself.

Radio appears to be in good condition but has two broken toggles on the front. The switches work, just the plastic toggle is missing.

Tom
W3TA

[G4XWDJim]

I dislike the expression ‘rare’. Usually intended to increase the thoughts of desirability in the mind of prospective purchasers.

There were only 200 or so built I’ve read. That may qualify as uncommon. A vlf receiver covering from 10 kHz to 600 kHz.

I had one for many years and used it to listen to the Grimeton alternator on 17.2 kHz.

It was also useful as a tunable IF or signal tracer for the lower frequencies. Not a lot of use as a band cruiser although an example of a nicely built receiver with 3 point alignment tuning on the lower bands.

I sold mine about 3 years ago for about £150.
Jim

[Radio Wrangler]

Hi Tom,

I found the manual and schematic on the web

https://rigreference.com/documents/r...92f74.82675127

There is a forum rule against discussing identifiable items on auction sites, and as 850s are not frequently seen, this comes under that rule. (It's in response to some past issues between sellers and bidders)

You might want to have a look at the Eddystone User Group website:

http://eddystoneusergroup.org.uk

They archive as much information as is available, and they maintain price guides. They also have for sale and wanted sections. Their guides are simple reports of completed auction prices, but may be several years old.

David

[trh01uk]

Originally Posted by thoyer454

I have a chance to buy an Eddystone 850/2. Not much on the web about them - rare I suppose?

There is one on the auction site for $5k dollars - is that what they go for? If so I may have to keep my couple hundred dollar offer to myself.

Radio appears to be in good condition but has two broken toggles on the front. The switches work, just the plastic toggle is missing.

Tom
W3TA

Tom,

the fact that you quote a price in dollars, suggests the item in question is located in USA. And of course, like all vintage receivers, this one will be a heavy item, and thus for any buyers in the US that's going to put the price up, since the cost - and more significantly, the risk of shipping from the UK is avoided.

However, you only have to look and see what other Eddystone receivers have sold for - here in the UK the typical price range is £50 - £200 - to see that the price you mention is way out of line. For that price, I would expect it to be personally delivered, proven fully working to spec, and with cosmetics like its just been taken new out of the manufacturer's packing! But then I'm not an Eddystone collector chasing such items.

I often get asked about finding items deemed to be "rare". And my observation is that nearly everything is out there somewhere - mostly stuck in someone's shed or attic and forgotten about. Usually until they die, and then someone else turns it all out. A proportion of that stuff finds its way to sales, small ads and auctions, and if you are keen to find such things, you have to be fully hooked into every possible sales outlet. Use such tools as "auction alerts". Make sure your friends know what you are looking for - send them photos so they recognise what you want. Use "wanted" columns, such as on this forum, and in other similar places. The real danger for the truly "rare" stuff is that no-one recognises what it is (even the so-called "experts"), and it just goes into the skip as worthless.


Richard

[trh01uk]

Tom,

the other observation I would make for anyone buying from overseas, as you might be if you buy an Eddystone located in the UK, is to pay for really good packaging. And by that I don't mean just a bit more bubble wrap in a 3-ply cardboard box. I mean making - or more likely buying - a wooden crate, designed for the job. Obviously the seller has to do that - but you as buyer have to be prepared to spend out the extra to make that happen.

When I shipped an RCA AR-88D receiver (weight around 96lbs I think) to Saudi Arabia not long ago, I insisted that the buyer pay for a commercially made wooden crate for it which I found on eBay. And the crate didn't cost a fortune - around £23 I recall - which was a fraction of the selling price of £150 and a fraction of the actual shipping cost which I think was near £100. It arrived just fine, exactly as I sent it.

Richard

[turretslug]

The low number produced probably justifies the description "rare" for once (I, too, dislike the sleeve-tugging deceit frequently associated with this term) but unless you particularly like Eddystones, it's not a particularly outstanding set technically. Essentially a good MW architecture tube-line-up radio with an LF coilpack, IMHO Racal's LF convertors represent a more elegant approach with their balanced topology (helping to prevent post-mixer circuitry being deafened by LO as the input frequency gets very low and keeping general sprogs down, but you'll need an RA17 to go with it....). For 5k, you could probably find an R389 and a specialist to make it tip-top!

Having said that, Eddystones do have a certain appeal associated with their solidity, neatness of construction and attention to mechanical detail, their electronics is just a bit pedestrian relative to how much they cost originally.

[thoyer454]

Originally Posted by trh01uk

Tom,

the fact that you quote a price in dollars, suggests the item in question is located in USA. And of course, like all vintage receivers, this one will be a heavy item, and thus for any buyers in the US that's going to put the price up, since the cost - and more significantly, the risk of shipping from the UK is avoided.

Richard

Hi Richard,

I am located in the US and radio is 30 minutes away from me. Shipping would be the back seat of my truck!

Thanks,

Tom

[thoyer454]

Originally Posted by turretslug

The low number produced probably justifies the description "rare" for once (I, too, dislike the sleeve-tugging deceit frequently associated with this term) but unless you particularly like Eddystones, it's not a particularly outstanding set technically. Essentially a good MW architecture tube-line-up radio with an LF coilpack, IMHO Racal's LF convertors represent a more elegant approach with their balanced topology (helping to prevent post-mixer circuitry being deafened by LO as the input frequency gets very low and keeping general sprogs down, but you'll need an RA17 to go with it....). For 5k, you could probably find an R389 and a specialist to make it tip-top!

Having said that, Eddystones do have a certain appeal associated with their solidity, neatness of construction and attention to mechanical detail, their electronics is just a bit pedestrian relative to how much they cost originally.

Thanks for the input. My main draw to this radio is the smoothness of the tuning and the layout.

I typically buy old radios based on what I like about them, mostly the looks or the mechanics, and not always performance. I like to clean them up and get them working then they usually get added to the collection. Very few leave the confines of my basement unless I need the room for a new aquisition.

Tom
W3TA

PS: I have one of those 389's..... Took me about a month of evenings and weekends to get it working as designed.

[thoyer454]

Originally Posted by Radio Wrangler

Hi Tom,

There is a forum rule against discussing identifiable items on auction sites, and as 850s are not frequently seen, this comes under that rule. (It's in response to some past issues between sellers and bidders)

David

Lesson learned and it makes sense. Thanks

Tom
W3TA

[Radio Wrangler]

There is an issue with VLF coverage on receivers, in that when tuning a superhet to zero hertz, the LO falls right into the IF at the first mixer (or only mixer) This gives you a whacking great signal.

Off tune a bit and some of the phase noise sideband energy still crosses the IF frequency and you experience a raised noise floor. So there is a trade off between how low you go and how extensive is the phase noise of your local oscillator. Synthesisers can be problematic in this respect. If you look at common general coverage receivers and transceivers with general coverage receive, you might look at the lowest tuned frequency allowed in software and consider this an indication of how much the manufacturer trusts the phase noise of his synthesiser ;-)

The RACAL RA1772 switches in a crystal filter to notch sideband noise at the IF frequency when the set is tuned low. This improves the noise floor very usefully. Richard, Guy and myself used the same trick in the HP3724A Baseband analyser when we designed its receiver structure. The 3724 had to tune down to 10kHz and maintain a specified noise floor, SFDR, and accuracy of selective level measurement.

In the LF/VLF area there are still a few broadcasters, Aviation navigation beacons, Grimeton on special days, and millions and millions of SMPS. Oh and the occasional stuff to hidden submarines. Is the Jim Creek transmitter still active?

I understand that LED lamps on the famous horse buggies are now usual in the electricity-free parts of Pennsylvania, but there may well be an SMPS buried between the battery and the diodes. You just can't get away from the things.

David

[turretslug]

Originally Posted by thoyer454

My main draw to this radio is the smoothness of the tuning and the layout.

I typically buy old radios based on what I like about them, mostly the looks or the mechanics, and not always performance. I like to clean them up and get them working then they usually get added to the collection.

Tom
W3TA

PS: I have one of those 389's..... Took me about a month of evenings and weekends to get it working as designed.

No issues with that Tom, that pretty much summarises my approach. There's a couple of Eddystones here, 670A and 750- not the greatest radios ever but the 750 is a nice band-cruiser, almost a daily driver and the 670A gives me the LW broadcast band that we Region 1 folk cling to as a sort of '20s comfort blanket (that's 1920s....). I'd sort of chewed over an 850, but it's heavy and bulky (deep) for its usefulness quotient and a bit rare.

Talking of classic Brit radios with looks and smooth tuning- if you have the patience to fettle an R389, that'd make good practice for a GEC BRT400. Similar straightforward single superhet as AR88 etc. but with refinement and finesse including amplified AGC but devilishly close-packed and a hot runner,

Colin

[dave walsh]

One of these was sold in the UK via a private on-line business that offers fully restored sets [or others needing work] two or three years ago. I'd never seen this Eddystone equivalent of a military VLF set like the CR200/B29 before . Although there were only a relatively few made, the Frequency Range is a bit of a clue as to why. You might pick up a marker beacon or a submarine perhaps. I think the price was around £200, certainly not more than 300 and as for several thousands Very specialised and limited use I would think but I wonder how the nearby seller has arrived at his price? I doubt there will be a stampede.

I struggled a bit with my B29 until I realised it's the only set in the CR range that is a TRF!!. [I think the 850 is a Superhet design]. Maybe David's usual clear analysis [post 10*] explains the war time choice of a TRF for the Marconi RX.

Dave W

[Dave757]

Hi,

It all depends what you want the set for. If it's just an investment on a shelf,
that's fine, - but 5K$!. And they aren't a bad set either, but they won't do anything
that a LF converter in front of a modern radio can't.

Now, if you want a rare Eddystone, try the ECR. I had a play with one about 20 years ago,
and it really wasn't very good. but it still sold a few weeks later for £1000.
The new owner had no hesitation in parting with the money, (regretfully not to me!),
having come over especially from Scandinavia to buy it.

I wonder if he's still got it! - I bet its worth more than £5000 now, let alone dollars.

Kind regards
Dave

[Dave757]

Originally Posted by dave walsh

I struggled a bit with my B29 until I realised it is the only set in the CR range that is a TRF. I think the 850 is a Superhet design.
Dave W

Hi Dave,

I struggled a bit with my CR200 too, - getting it up 26 stairs to
my shack at the top of my 3 storey townhouse in Brum.

Trouble was I was about 20 years older when I moved to Norfolk,
and I think if I had tried to carry it down the stairs I would not
have made it here, so discretion was the better part of valour and I
gave it to another radio ham, and he collected it!

I still miss it, and much preferred it to an 850, I mean, - what's not to
like about a TRF with a BFO!

Now, as I'm in a bungalow, if a nice RCA RAK receiver came along
I might be tempted, the only struggle then would be getting it past the missus !

Kind regards
Dave

[trh01uk]

Originally Posted by Radio Wrangler

There is an issue with VLF coverage on receivers, in that when tuning a superhet to zero hertz, the LO falls right into the IF at the first mixer (or only mixer) This gives you a whacking great signal.

Off tune a bit and some of the phase noise sideband energy still crosses the IF frequency and you experience a raised noise floor. So there is a trade off between how low you go and how extensive is the phase noise of your local oscillator. Synthesisers can be problematic in this respect. If you look at common general coverage receivers and transceivers with general coverage receive, you might look at the lowest tuned frequency allowed in software and consider this an indication of how much the manufacturer trusts the phase noise of his synthesiser ;-)


David

In the case of the 850/2 its a totally standard superhet with 6BA6 RF stage, 6AJ8 mixer/local oscillator, followed by two more 6BA6 IF stages. The IF is at 720kc/s.

Your comments above about phase noise no doubt explain why the overall sensitivity is only quoted as 5uV on CW for 15dB S/N ratio for all frequencies. That's hardly good when most HF receivers are better than 1uV.

The AM sensitivity is quoted at 5uV for 15dB S/N ratio, but only above 100kc/s. This again is hardly stunning, and I note that the sensitivity at the mixer grid at the IF frequency is 16uV or better, so the RF and mixer stages would appear to only manage 10dB gain - more likely phase noise limitation as you say.

Richard

[Radio Wrangler]

Phase noise scales with frequency at 20dB per decade. This is true whether you use a frequency multiplier or divider. It is also true if you compare oscillators having the same resonator Q if the active device noise figures are equal.

To cover next to nothing up to 600kHz in a superhet forces an upconversion architecture to an IF higher than the top of the coverage. The local oscillator must then tune this IF value higher than the coverage. So, the higher the chosen IF, the noisier the LO becomes for a given LO technology and components. So a receiver with a 720kHz IF has an advantage over a general purpose VLF-HF set with a high IF (>30MHz). This is the advantage that amateur bands only receivers with their typically 9MHz IF have over the general coverage upconverters with their higher IFs.

TRFs have their difficulties, but this is the area where they show advantages. You can always view a superhet as a TRF made for an easy, fixed frequency, with a frequency converter stuck on the front.

That said, there is little point busting a gut to get receiver noise very low as natural noise from the atmosphere and astronomical sources increases with decreasing frequency.

David

[Synchrodyne]

Originally Posted by Radio Wrangler

That said, there is little point busting a gut to get receiver noise very low as natural noise from the atmosphere and astronomical sources increases with decreasing frequency.

As illustrated by the attached chart:




Cheers,

[trh01uk]

Originally Posted by Synchrodyne

As illustrated by the attached chart:

Attachment 217653


Cheers,

Hmm, the chart shows increasing noise as frequency falls, however the figures shown don't mean a whole lot to me. 60dBuV/m at 100kc/s. Or 1mV/m. Sounds a lot, but what does one get out of a serious LF/VLF aerial, given the usual size limitations? I mean what antenna factor can we expect at this sort of frequency?


Richard

[trh01uk]

And as a follow-up comment on LF/VLF noise, I found this rather interesting scan of the LF bands from 14 to 62kHz, on some unidentified receiving system, using a 150' long wire: https://www.radiomuseum.co.uk/VLF%20RECEPTION.html

The very low signal voltages in dBm may just indicate that the antenna factor of such a wire is very poor at such a low frequency. However I also note that the noise floor appears to be going in entirely the opposite direction from the one in Synchrodyne's graph. In other words the noise appears to be falling with falling frequency.


Richard

[Radio Wrangler]

Don't worry too much about the receive path's antenna factor because it'll be the same for the signal and for the noise, so you still get a manky signal to noise ratio before the receiver factors in.

And as atmospheric noise at 10kHz is about 40dB higher than it is at 1MHz, you'd need a very nasty receiver noise figure to become the limiting factor. It's normally phase noise that does the deed.

David