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 Post subject: SOE Clandestine receiver - more info.
PostPosted: Sep Tue 16, 2008 2:23 pm 
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Location: Littlehampton England
This is to answer questions I have been asked following my previous posting. { Moderator added: Previous posting available here http://antiqueradios.com/forums/viewtopic.php?t=96007 }

Winding the coil was easier than I expected. Once the old wire was removed and the former cleaned up various holes revealed themselves. These were spaced at 120 degrees around the former, hence the reference to thirds of a turn that FM Refugee spotted, and about the right distance apart to get the 25 and 18 turn sections nicely placed. I guessed the wave wound coil would be about one eighth of an inch wide and spaced it where I thought it should be. Never having seen an original coil I can't compare it but the results seem very good.
The wave wound coupling winding was quite large I thought for its frequency coverage but the set would have been intended for use with short and makeshift aerials bearing in mind its intended purpose. With 5 feet of wire as an aerial hung up my kitchen wall it brought in hundreds of stations during an evenings listening. Its coverage is 6 to 12 megs and SSB amateurs on 40 metres came in well. Tuning SSB is a delicate operation with the set just oscillating but worked very successfully.

I know I've fitted modern components which many would consider sacrilege but the owner wanted to relive his youth and this set must fulfil that ambition for him because electronically it is standard.

Several friends have decided to make a replica because it is so unusual . When I make one I think I'll use a smaller tuning capacitor, preferably with ball bearings and a better ratio slow motion drive. The one used is 5 to 1 making for very delicate tuning. A bigger knob would help too because we can't seem to resist DXing.
I'd also experiment with the anode load and bias voltage on the output valve to get a little more grunt out of it. This set I would think did its job very well in listening to the wartime BBC and achieving one of its principle objectives of low battery consumption.

Here's a pic of the chassis layout. I hope you can see it well enough to understand it. I drew it purely for my own use to supplement my memory and as such it may be lacking detail. I've saved it as A4 size so presumably if you can display it as A4 size you may be able to scale off it.

Image


This is a black and white pic from the book Wireless for the Warrior No 4

Image

For those who read Radio Bygones it also appeared there I think, in issue 54 in 1996.

Jim


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 Post subject:
PostPosted: Sep Tue 16, 2008 2:31 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
How microphonic is it? Some of those battery tubes were very microphonic, especially when followed by two audio stages.
Curt

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(Connoisseur of the cold 807) CW forever!


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 Post subject:
PostPosted: Sep Tue 16, 2008 4:34 pm 
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Forum Policy Reminder - when continuing a discussion about a particular subject, please post it as a reply to the original topic rather than starting a new thread about the same topic. This way the discussion doesn't become separated and scattered throughout the forum.

Thanks,
Dave


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 Post subject:
PostPosted: Sep Tue 16, 2008 8:48 pm 
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Joined: Jan Wed 23, 2008 2:55 pm
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Location: Littlehampton England
Sorry Dave,

Would you like to move it or shall I re-post it as a reply so that you can delete the unwanted one. I was pleased with myself too for having worked out how to post pictures.

Curt, yes it is microphonic but not to the extent that it causes difficulty in hearing stations. The original users weren't DXers either.

Jim


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 Post subject:
PostPosted: Sep Wed 17, 2008 2:12 am 
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Location: Brunswick, ME 04011 (USA)
*scratching head*...where did that 2.2µF cap come from? A sort of 'production change', perhaps? Is it on the -4.5V source? (The plans in the original thread only reference one electrolytic: C13, 1µF 200V, on the +30V source. Did they add a C14, presumably a 2µF, at a later time?)...


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 Post subject:
PostPosted: Sep Wed 17, 2008 4:20 am 
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...some more thoughts on that coil, based on the different pictures, measurements and calculations:
...We know the form to be 1/2 inch outside diameter and, based on that, I calculate it to be about 1 3/8 inches long, including the 'flange' at the top that has several connecting pins in it.
...Based on the 'Wireless for the Warrior' photo above: The 80-turn 'wave' winding at the bottom looks to be about 1/4 inch wide, then about a 1/8-inch space, then the 25 1/3-turn single-layer winding, then another small space (1/16 inch or less), then the 18 1/3-turn single-layer winding. This leaves a 1/8-inch or so space at the top of the form underneath the 'flange'.
...The coil has a tuning slug inside the form (composition and dimensions not specified) attached to a threaded and slotted stud for tuning. Apparently the bottom of the form is closed, with a threaded hole in the center for the tuning stud. A locknut is added to prevent detuning.
...The plans shown in the earlier thread called for 'D. S. C.' wire, but I can't be sure whether that was an English or a Norwegian abbreviation or what it stood for.

...I hope these observations are accurate enough to help anyone trying to build a replica of this very interesting little set...I'm sorely tempted to try it myself someday...if I can get hold of some of the parts...


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 Post subject:
PostPosted: Sep Wed 17, 2008 11:10 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
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Location: Sandpoint, IDAHO 83864
I believe D.S.C. stood for Double Silk Covered. In other words, it was a wire insulated with two wraps of silk for insulation. Each layer of silk was wound in opposite directions so it would not bunch up. That type of wire at one time was very popular and was the choice of coil winders. Another was D.C.C., which was Double Cotton Covered.

Look thru old magazines and books dating to the 1920's and 1930's and you will see reference to those terms quite often when it comes to the coils.
Curt

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(Connoisseur of the cold 807) CW forever!


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 Post subject:
PostPosted: Sep Wed 17, 2008 2:30 pm 
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...that sounds familiar, Curt. Can you even find that kind of wire in those sizes anymore?...wouldn't using modern enamelled wire throw off the coil dimensions a bit because the extra thickness of the double silk coating is not there?...


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 Post subject:
PostPosted: Sep Wed 17, 2008 2:36 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
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Location: Sandpoint, IDAHO 83864
I think the last time I checked, AES had some small quantities of it, but it was horrible in the price department. I don't think any wire manufacturer makes it any more, and if they did, it would have to be on a special order basis with a large minimum buy.

I find it at hamfests once in a while, but not as common as it used to be. I buy up bits and pieces when I can that way, and I have several spools of it that have small remmants left. Only none of them have enough to wind a decent coil!
Curt

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(Connoisseur of the cold 807) CW forever!


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 Post subject:
PostPosted: Sep Wed 17, 2008 3:23 pm 
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FM Refugee wrote:
...that sounds familiar, Curt. Can you even find that kind of wire in those sizes anymore?...wouldn't using modern enamelled wire throw off the coil dimensions a bit because the extra thickness of the double silk coating is not there?...


Not so much as to be a problem. The inductance values are given so you could tweak it a turn or two as needed . Plus its a tunable coil.


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 Post subject:
PostPosted: Sep Wed 17, 2008 5:35 pm 
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Location: Southern NH, 03076
Jack Shirley wrote:
FM Refugee wrote:
...that sounds familiar, Curt. Can you even find that kind of wire in those sizes anymore?...wouldn't using modern enamelled wire throw off the coil dimensions a bit because the extra thickness of the double silk coating is not there?...


Not so much as to be a problem. The inductance values are given so you could tweak it a turn or two as needed . Plus its a tunable coil.



Thats what home brew is all about and not 100% duplication building. Even one or two sizes difference in wire size wont make enough difference to measure. The form can even be different within reason.

Carl


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 Post subject:
PostPosted: Sep Wed 17, 2008 8:06 pm 
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Joined: Jan Wed 23, 2008 2:55 pm
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Location: Littlehampton England
Curt is right. DSC is double silk covered and the wire gauge specified is SWG, standard wire gauge not the American standard. I think your gauge is slightly thinner for the same number. I have several spools of it but like the rest of my stuff it's temporarily lost until my house move is finally "complete".

I did wind the coupling coil in too narrow a pile I realised after I'd done it. I used second hand enamelled copper wire in three different gauges that I took off old Post Office relays as I wound it on to the bakelite former. I was so pleased at finding a way to "wave wind" by hand I didn't look at it properly. I wound the turns clockwise as viewed from the tags end. I set the inductance value right by pruning the coil and after screwing the core where I thought a good starting point should be it came within 50k/cs of its frequency. The core material is unknown but looks like iron dust and is about 3/8" diameter and 1/2" long on a 4 BA brass screw. I can't imagine the original coil working any better than my homebrew effort as results are so good.

I would advise a better quality tuning cap than a trimmer with an extension shaft like this one has. A nice ball bearing one of half the capacity to make the tuning easier with a good slow motion drive would make it very pleasant to use.

The whole set is so light that it tends to move about whilst tuning. Standing a weight on it would help.

I'd very much like to see any replicas that are made from this info.

Jim


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 Post subject:
PostPosted: Sep Thu 18, 2008 2:48 am 
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Location: S. Dartmouth MA 02748-1225 USA
Jim,

I checked the attic this evening and found the following coil form:

1/2" OD, 3/8" ID, 2-3/64" long, no holes except down the center. Material is hard, dark amber phenolic. Original source box was marked Amphenol RS8.

There is no ferrite core or means of mounting, essentially, it is a phenolic bushing...

I have 63 of these "forms" that I will make available to anyone who desires to follow through making one of these interesting sets. Obviously some experimentation will be required to fabicate a coil that functions correctly with this form.

Best,

Chas

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 Post subject:
PostPosted: Sep Thu 18, 2008 8:40 am 
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Location: Littlehampton England
Chas,

Thanks for the thoughts. The former in the set is located by a very short octal valve type spigot on the rear end which protrudes through the rear paxolin panel and is held in place by a large-ish washer and nut on the core adjusting screw.

Jim


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 Post subject:
PostPosted: Sep Thu 18, 2008 4:08 pm 
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...that 'paxolin' (phenolic?) rear panel has on it, from left to right: the coil, two jacks (phones, I presume), the battery supply wires, and...what? at the left end...


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 Post subject:
PostPosted: Sep Thu 18, 2008 4:32 pm 
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Joined: Jan Wed 23, 2008 2:55 pm
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Location: Littlehampton England
Looking from the rear the paxolin panel has a very rare bakelite slide/wedge connector for the headphones, made by the Brush Company at the left hand end. This had been so damaged that it was not usable but I left it in place for authenticity and connected the one spare wire of the four core lead I used to feed battery supplies to the set from the battery box, as the headphone out lead to the jack sockets in the battery box for convenience and reliabilty of connection. I later secured the four core lead to the back of the set with a clamp.
Next along on the paxolin panel are eyelets through which the battery leads pass and then are two small banana type sockets for aerial and earth. Then finally comes the coil slug adjust screw.

If anyone would like a better close up of the set let me know and I'll take more pics and post them here.

Jim


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 Post subject:
PostPosted: Aug Sun 23, 2009 5:09 pm 
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Location: Littlehampton England
Folks,

For those who showed interest in my repair to this set last year there is an original one for sale on the British eBay. A very nice set and looks quite complete. Wish I'd seen it before I started work. 270445938382

Jim


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 Post subject:
PostPosted: Aug Mon 24, 2009 3:40 pm 
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Because that is an unusual and historically important set, it would have been better to put the new capacitors in the original sleeves.

Clandestine radios are lots of fun. The designer of that one was probably very proud of the whiskey flask size and shape.

Here's the auction link: http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 3D1&_rdc=1


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