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 Post subject: Stoddart VLF & HF Receivers: Connector & Other Quest
PostPosted: Aug Wed 08, 2007 11:20 am 
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I have an IM-36/URM-6 (Navy version of the NM-10, 14 – 250 kHz) with matching power supply, and an NM-20A (150 kHz – 25 mHz). My questions:

(1) Where can I obtain the five-conductor cable that connects the power supply to the NM-10, or the screw-on connectors with which I might make up my own cable (one is male, and the other female)?

(2) I presume that the power supply for the NM-10 will also work with the NM-20 (the power connectors are the same); am I correct?

(3) The loop connectors on both receivers resemble a small version of the old screw-on UHF connectors, but with two central conductors. What are these connectors called, and what is a good source for them?

(4) The aerial connector on the NM-20A resembles the loop connector, but is larger (approximately the size of a UHF connector), though the two central prongs are much thinner than on the loop connectors. What is this style of connector called, and where might they be obtained?

(5) Does any-one know of a source of the loop for the NM-20A?

(6) Does any-one know of a source of manuals for these receivers (there is not even a Stoddart section on the BAMA web-site, and the military gear section does not list them)?

:?: :?: :?: :?: :?: :?: :?: :?:


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PostPosted: Aug Wed 08, 2007 3:19 pm 
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Hi Philip,

I was expecting Alan Douglas to jump in on this one, but perhaps he's snoozing. :D

AFAIK the NM-series used standard military MS-series connectors for power and control. These are still available from Allied, Newark, and other major online vendors.

Look for nomenclature stamped into the barrel of the connector just above the mounting flange. There should be a number such as MS3102A14S-2P. The exact format will differ slightly. The last character is the gender: S = socket; P = plug.

Just look up that number with the correct gender and shell configuration and you have your connector. They cost ~$20, but it varies with the configuration.

URLs:
Allied: http://www.alliedelec.com
Newark: http://www.newark.com
Mouser: http://www.mouser.com

As far as accessories and such, these show up on evilpay all the time.

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PostPosted: Aug Wed 08, 2007 5:52 pm 
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I was out trimming brush and pulling poison ivy, on a day off work.

I believe the power supplies are the same but I only own an NM-10A, not a 20. Actually I think I have two 10s. I've managed to find manuals for the 10A but they're fairly large and I can't get too excited about xeroxing them (not to mention that the good xerox machine at work is right next to the boss's desk, and he eats lunch there too).

The twinax connectors (the larger one) were popular for computer networks and I have lots of those. The smaller one that looks like a PL259 is harder to find.

What I'd really like is to move my Stoddart collection on to a new owner, as it's taking up space in the bedroom and is rarely used. There are four in the series, 10, 22, 30 and 52 as I remember, and four power supplies (and manuals).


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PostPosted: Aug Thu 09, 2007 11:28 am 
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Leigh, many thanks for your help. Despite decades of radio collecting, I have had minimal experience with military style equipment and the associated connectors. I had not noticed the markings on the mounting flanges of the panel receptacles, since they were very lightly impressed. And while I had none of the cable-end connectors for the five-conductor receptacles, I did have one for the A.C. input receptacle (which is the same, but with a three-conductor insert), and after reading your explanation of nomenclature, I could extrapolate from its numbers. As a result, I was able to determine the connectors I need 8) , and for the benefit of other readers, I shall post the numbers here.

Power output receptacle on Stoddart power supply: MS3102A14S-5S
Connector for cable to attach to above: MS3106A14S-5P
Power input receptacle on Stoddart receivers: MS3102A14S-5P
Connector for cable to attach to above: MS3106A14S-5S

I found that both cable-end connectors are available from all three of the firms you suggested, at similar prices. :)

Alan, thanks too for your help. I recall reading your comments on the Stoddart VLF unit on one of the forums here, some time ago. The term ‘twin-ax’ struck a chord in my memory, and I was pleased to find that these connectors are still commonly available. I found numbers on the flanges of the ‘mystery’ connectors that resemble the PL-259 UHF connector. One of the panel receptacles was marked NT-49194, and another, FSC-91836. These numbers bring up nothing on the web-sites Leigh mentioned. The NM-10 came with a short link of cable with connectors at each end, but these have no numbers stamped on them. However, there is also an Amphenol right-angle adapter marked PL-293 over UG-104/U. Perhaps some-one will know what the related connectors are termed.

I certainly would not mind giving your Stoddart units a new home, but I expect it would be costly to ship all of the items, never mind the cost of the instruments themselves. :shock:


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 Post subject:
PostPosted: Aug Thu 09, 2007 6:08 pm 
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Hi Phil,

Glad you found the MS connectors. For future reference, the first part of the number (MS3106A) defines the shell. The second part (14S-2) defines the insert, which is the pin configuration. The suffix S or P is the gender as mentioned above.

The UG-series numbers are mil-spec designators. Anybody's UG-104/U should work for the same function and be interchangeable.

I tried the online vendors and nobody has these any more. I don't believe they've been used in any recent designs. IBM used a twinax cable for its System/3x high-speed terminal interface, but that was 93 ohm impedance.

Surplus Sales of Nebraska has some of the accessory items including your UG-104 here http://www.surplussales.com/Connectors/UHFTwin.html
but I don't find any chassis or cable-mount connectors in that series. It would be worth an email exchange with Bob Grinnell (the owner) to inquire about them. grinnell@surplussales.com

You could also try Fair Radio Sales in Lima Ohio http://www.fairradio.com
They're a major source of military electronics.

With both surplus vendors, tell them that these are for a Stoddart NM-series receiver. They may have original manufacturer's accessories which are not inventoried by the connector number.

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PostPosted: Aug Fri 10, 2007 11:46 am 
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Thanks, Leigh, for the additional information. I was actually quite amazed to see the Surplus Sales page you found; I was unable to turn up any items for sale in the “twin-UHF” format, on internet searches. I have book-marked that page, and will very likely do as you suggest.

I had done some very broad searching on the Fair Radio web-page, without luck. But after reading your last message, I thought of simply entering the term “Stoddart” in the search box, and was pleasantly surprised to find that there is a reproduction manual available for the VLF unit!

Alan, if I resided anywhere near you (I live on Long Island, New York), I would follow up on your suggestion.


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 Post subject:
PostPosted: Aug Fri 17, 2007 1:35 am 
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Philip - I also have an IM-36/URM-6 (14-250 kHz). I bought it at the Mil. Radio Collectors Group meet at Camp San Luis Obispo in May of this year.

Another vendor had the 5-pin power conector but I need the pinout and associated voltages so I can build a PSU. Do you have this info?

Needs the loop antenna (naturally).

Thanks for the antenna connector info, Gang! I wanna hear some 'spherics live!

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PostPosted: Aug Fri 17, 2007 1:59 am 
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Jim- what happened to the MRCG annual meets at Ft. McArthur? I know they used to meet in San Luis Obispo, but due to security reasons couldn't for a couple years. I have VHS videos of several of their meets that were taken by one of their members who had a K6 call, but darned if I can't remember him at the moment. But if you see any of the group tell them hello from me. I assume that Dennis DuVall is still heading up the group?
Curt

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 Post subject:
PostPosted: Aug Fri 17, 2007 6:06 am 
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Jim,

As you no doubt know, these connectors use letters to designate terminals: these letters are moulded into the insulator inserts, and will be clockwise on the male connectors (those with pins), and anti-clockwise on the female connectors (those with sleeves). The connexions are made according to the letters. The letter “A” is at the 12:00 position, with the indexing tooth or notch at the same position.

The power supplies for the NM-10, and many others of the Stoddart line, have the following terminal voltages:

A = 6.3 V.A.C. (filament).
B = +225 V.D.C. (B+).
C = -60 V.D.C. (C- bias; this is a regulated voltage).
D = Earth/Ground/B-/C+
E = 6.3 V.A.C. (filament).

Actual measurement with a Fluke digital multi-meter disclosed 227 V.D.C. B+ from my NM-10 power supply, unloaded, and 60.1 V.D.C. C-.

I may be able to help a bit on the construction of a loop for the NM-10. The Stoddart loop is shielded inside a metal tube loop (apparently, low-ferromagnetic stainless steel). The loop itself is made of enamelled magnet wire wound on a hoop made of phenolic strip. The radius of the hoop is 2.625 inches. The magnet wire measures 0.010 inch in diameter (taken with a vernier calliper under less than ideal circumstances—I did not wish to put pressure on the fine wire; I could not fit a micrometer into the opening). This measurement includes the enamel coating, so the wire is likely 31 gauge (0.0089 inch, bare). Since this wire has a resistance of 130.1202 ohms per thousand feet, or 0.1301202 ohms per 12 inches, and the resistance of the loop measures at 6.7 ohms on the Fluke digital multi-meter, it is possible to calculate that there are approximately 37.46 turns, closely spaced (as can be seen through a hole, but not well enough to actually count). With a winding length of about .370 inch, this calculates to an inductance of about 353.86 uH. There is a 10% tolerance mica condenser of 470 pF connected across the loop, in the loop assembly itself. The resonant frequency of these values is 390.26 kHz, which is above the range of the NM-10, as one would expect. I have not had a chance yet to actually measure the resonant frequency of the loop and condenser.

I have not found a source for the twin-UHF type connectors used for the loop and aerial on the NM-10. My NM-20 has this connector for the loop, but a different connector for the aerial (apparently “Twin-Ax”).


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 Post subject:
PostPosted: Aug Fri 17, 2007 9:34 pm 
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Stoddart and MRCG:

Plilip - many thanks for the voltages and antenna info. I have an existing PSU that will provide all except the C-.

Hmmmmm.......maybe a VR-75 and some dropping resistors :lol: ? Gotta be hollow state. Maybe a stack of 9V cells and a rheostat for starters.

For the antenna, I may try one of the shielded VLF/ULF/ELF designs on the web.

I have a Rycom R1307A/GR (~3-812 kC) but it won't get much past 200kC w/o a shielded loop (which I haven't built yet). If you are a "lowfer", can you recommend any of the solid state homebrew RX designs? I have power lines on 2 sides of my lot :evil: and will need to get out into the hinterland on battery power if I am to ever hear anything :roll: . (please excuse the emoticons, I couldn't help it, I swear!)

Curt - This was the first MRCG event I've attended. Don't know of Ft. McArthur. It was like going to my first 12-step meeting......now I don't feel so alone with my affliction.......... :lol: :lol: Dennis has a DVD available for this years meet at $10.

I did very well at the swapmeet. Picked up a working, tagless BC-312 (may be an "L" from its layout) for $20. The dynamotor was bypassed for direct connection to a PSU. Needs aligning, and a check of the dyno, but fun to play with.

Also bought a TBW-4 (no modulator) for $20. It's tubeless and both big roller unductors have been stripped of their wire. Looks OK, otherwise. That one will be a challenge to power up.........but what a riot when I do!

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Jim Falls
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 Post subject:
PostPosted: Aug Sat 18, 2007 9:22 am 
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As a result of some experiences last night, I can offer a bit more information. I obtained a Stoddart power switcher. This enables one Stoddart power supply to power any one of four receivers, selectable by a rotary switch. Three filament transformers are provided, to keep all sets warmed up. I was thus able to try out my NM-10, which worked perfectly.

What a superb receiver! The 15.734 kHz horizontal scan signal from a television set in another room came in at full deflexion on the meter, and the various harmonics were almost as strong. This points up the need for a noise-free environment, which I hope to attain when I relocate to a rural area. An ESR testing adapter I constructed some years ago (with a micro-power 140 kHz oscillator employing a single germanium transistor) happened to be at hand. Turning it on several feet away drove the meter off-scale, when the set was tuned to 140 kHz. I heard a number of interesting signals, including a very strong repetitive signal at 19.5 kHz, which had notable mains-frequency modulation.

Then, after about forty-five minutes, the dial light flickered and in an instant the receiver went dead. Both fuses in the power supply had opened. It soon turned out that one of the electrolytic condensers on the B+ circuit, a 4 mF 600 WVDC type, had a dead short-circuit. Several days ago, I had tested the power supply, bringing the A.C. input voltage up very gradually with a variable auto-transformer. I then let it run for quite some time without incident, but it is now clear that the condenser was marginal. Fortunately, it did not explode when it short-circuited. 600-volt electrolytic condensers appear to be hard to find these days, so I am considering using a 440 VAC non-electrolytic fan motor condenser as a replacement.

Since I had to have at least a brief look inside the power supply to find the source of the trouble, I can say that the B+ supply is regulated with a pair of gas regulator tubes. The regulator for the C- appears to be a large neon lamp with a bayonet base. This supports your VR-75 idea; that is a neon-filled tube which could certainly be used as you suggest. I am afraid I was in too much of a hurry to record the type numbers of the neon lamp or the VR tubes. But I can say that the B+ rectifier is a 5Y3 and the C- rectifier is a 6X4.

I have read somewhere that the nominal B+ for the Stoddart receivers is 250 volts. It is possible that the condenser was already failing and drawing down the voltage when I measured 227 volts. However, the radio did work perfectly.

Despite long interest in VLF, I have not had the opportunity to engage in many activities. I have a Radiomarine AR-8510 TRF/regenerative receiver that covers 15 kHz to 650 kHz and works very well, and a Rohde & Schwarz Tunable Indicating Amplifier type UBM BN12121/2 that covers 45 Hz to 600 kHz.

For portable use (which makes sense, in order to find a low-noise location), a solid-state VLF converter for a portable short wave receiver could be used. Some commercial VLF receivers, such as some Rycom units other than your excellent tube-type model, are battery powered. But it would not be too much of a problem to power tube type units with batteries, especially those that use external power supplies and thus have convenient power connectors. Indeed, I have not operated the Radiomarine unit with anything but batteries.

There is a very interesting web-site on the low end of the VLF spectrum, and it includes descriptions of home-made equipment:

http://www.vlf.it/


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