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Military Collector Group Post Backmail #28 (18 pages) Index; PC BOARD MAKEING FOR DUMMIES KEN NEEDS A HUMMER SEM-52A, SOME HELP IN PROGRESS SEM-52A DATA; by Alan Tasker THE GERMAN SEM-52; By Alan Tasker REVISED SEM-52 DATA; TG-5??? HT-2A??? ÍMetallsuchgerate MSG 75Î,by Bill Howard MAGIC EYE TUBES; by John Mackesy *********************************************** PC board design & etching for dummies: I know this is a bit off the subject of our group. But a member of us is going into small scale production of items we all need. And as I didn't want to sit here for 3 hours & write this all out for one person,I'm gonna make you all read it! OK here goes. The easiest way is the direct method,it's OK for low production,& best for us simpletons,but pain in the but for high volume production. For this you need only ; SHOPPING LIST; #1,etchant #2,non photo sensitive PC board material #3, are a "Sharpie" fine point permanent marker #4,flat plastic tray,transparent preferred,large enough for boards #5,desk lamp is nice,one on a goose neck,not florescent,needs be bright & sometimes hot. #6,agitater,(discussed later) #7,.01inch graph paper. #8,other misc hardware,such as drill, bit(max size 1/16),very sharp awl,fingernail polish remover. Dremel or other small jig saw,etc. DESCRIPTION,& EXPLANATIONS; #1,etchant can be had at numerous places,even sorry to say,Radio Shack. More expensive there though(typical) the stuff is pretty cheap though,especially with some mail order vendors.. #2,PC board material,copper clad,you only use the photo sen stuff when doing the negative process,board material can also be had at radio shack,as well as numerous surplus & mail order places. I bought some 4 x 8 ft sheets one time at a GSA sale from a guy who'd just pay'd $200.00 a sheet for it,he though it was solid copper,HA HA,needles to say,he didn't get his money back. #3,"Sharpie",You can get regular etch resistant pins,but they are exactly the same thing,but at three times the price. For larger trace areas a normal magic marker will work. For the really fine ones,you can take a razor blade & cut the felt down on the Sharpie. I usually got several,all sharpened to different points,stay away from the little groove down the side when you do this.. #4,tray must be plastic or if your really up town,glass. transparent is preferred because it will allow you to hold a bright light under it. If the etching process is complete,the light will show through the PC board material very nicely. Otherwise you must remove the PC board from the gue & hold it up to the light(messy). #5,A bright desk lamp is needed for two things. First you use it to tell when the boards are done etching,it will shine threw the board,if you can't see light threw it,it ain't done.. Second for heat,if your impatient,you can positions the lamp directly over the etchant tray, this will heat it very slightly & speed up the etchant process,also giving you a more consistent etching time. This also good practice with some cheeper board materials because the copper clad thickness isn't very uniform.Thus in places you might eat away the trace area before the none trace areas are finished. #6,You need something to agitate the board,here your imagination,& ingenuity must work because I can't draw you a picture. You can just run back and forth to the tray & wiggle it once in awhile,but this a pain in the "A". You can also just let the stuff cook & not mess with it,but this won't always work. As the copper is etched away from the board,it will just lay there. This does two things,one it prevents you from using the light to see threw it. Second it prevents further etching,I/E the etched copper lays there & protects the unetched copper. If not agitated you run the risk of uneven etching & a messed up board. Once I needed a board done,only one & in a hurry,so I took my 1/2 sheet sander,stuck it in the vise upside down,hooked it to a variac,& placed the etchant tray on the sanding pad. This worked well,but made a bunch of noise, & if you wern't very carefull,the tray would vibrate off the sander. You don't ever wanna let this happin to you!. Best thing I've found is a barbecue rotesory(or whatever the damn things are called),every garage or shed has a couple of them,& "nobody ever uses them". These things turn at 1rpm,haf plent of poop & are perfect. I'll let you figure out the mechanics. One simple method,a 1/4" bolt will go strait threw the square hole,you can put a piece of flat metal on the end of this about 1/2" wide & 2" long(hole drilled in the center). This is placed under the end of a board,the other end of this board is hinged. The rotesory(or whatever the damn thing is called) will then cam the end of the board up & down a distance you determine(about an inch) dependant on board/tray size & how deep your etchant is. This will all take place at about 2rpm,& works perfectly. #7,.01inch graph paper. You use this stuff to design you board trace. .01 inch is industry standard for lead spacing on most electronic parts,including IC's,axial lead capacitors etc. PROCESS; Now you got all your crap together,& circuit you want to reproduce. You first lay everything out on graph paper. Placing components as they need be,you experiment getting point A to point B without crossing traces,this is sometimes difficult to do particularly when using IC's but it can usually be done with a minimum of jumpers,if any. What helps immensely is .01inch graph paper as this is actual size. You may want to use 1/4 inch paper to lay out trace design,particularly if it is a complicated one. Once your board/trace design is completed & on .01 graph paper. You lay this onto PC board material,copper side up(be sure you do not reverse what you've designed). Taking your very sharp awl,you penetrate paper where component leads will be,marking it for drilling. Don't bother trying this with carbon paper or anything else,you'll just waist your time & make another mess. All needed holes are now marked & need be drilled. Regardless of needed hole size (usually less than 1/16),you will drill this first board with a 1/16 bit. This will be pattern for future duplications & 1/16 is minimum size that will allow you to use an awl threw(a good one for this purpose can be made from a piece of old stainless steel antenna rod). Once all your holes are marked & drilled,you simply get your Sharpie & connect the dots. Whatever you do,do not etch this first board. Once you've finished marking the trace,lay it aside & do another,using the first to mark holes only. Believe me,if you etch this first board,down road you'll run out of finished boards & use this pattern. You'll then hafta go threw all previous crap again. If it's not been etched,your not tempted. I've done it,more than once! Your boards are now all drilled & trace lines marked,we hope you remembered to put cap back on Sharpie because they will dry up in just a few minutes. Put boards in your tray,copper side up is usually best,& pour enough etchant in to cover them. You can position your lamp if used & turn on your agitating apparatuses. You want to check on progress in no more than 10 minutes to see how far it is along,& to insure that boards have not floated to top. average etching time depends on many variables including room temp,copper thickness,etchant age,etc. But may run as little as 15 minutes. Once all etching is done,retrieve your boards from the gunk,I use hemostats for all handling. Run to the sink & rinse off the boards & hemostats. Use fingernail polish remover to clean the ink off,or steel wool if necessary. A word about fingernail polish remover,if at all possible do not get the sented stuff unless you want a horrible head ache,how the females can stand this stuff is beyond me! Do not poor out the old etchant,put it in a suitable container & place it in the ice box. All contaminants will this sink to bottom,& it can be re-used when all the fresh stuff is gone. Also at all cost don't get it on anything,it is a mild acid but this isn't the trouble. It's worse than iodine about staining,& it will stain ANYTHING. I know all this sounds like a bunch of time & trouble,but Believe me,even if your only making one board,it's still less pain in the ass than using perfboard & direct wiring. Besides,it will look much better,& less like a 10 year old had made it. A tip for us vain types,reserve yourself a little room to put your J Handcock in the corner with the Sharpie. Also all the area on the board that will not be used,should be inked over. This will save etchant contamination,shortin etching time,& you never have enough ground trace anyway. Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN *********************************************** KEN WANT'S A HUMMER; On Sat, 12 Jul 1997 22:06:14 -0700 kenscom@juno.com (KEN F SAKAMOTO) writes: >DOES ANYONE OUT THERE KNOW THE STATUS OF SURPLUS HMMWV'S? I HAVE HEARD SEVERAL RUMORS - SOME SAY THAT THEY ARE SCRAPPED DUE TO AN AGREEMENT WITH THE MANUFACTURER NOT TO RELEASE TO ANY USER. OTHER SOURCES SAY THEY ARE AVAILABLE FOR REUTILIZATION TO OTHER GOVT. AGENCIES. I DREAM OF FINDING ONE FOR OUR FIRE DEPT. FOR SEARCH AND RESCUE PURPOSES. WE ONCE HAD THE USE OF ONE (M998) FROM THE ARMY RESERVE AND IT WAS PERFECT. MY OWN OPINON IS THAT IT IS NOT SUITABLE FOR A FIRE VEHICLE IN CALIF. DUE TO THE LIMITED CARRYING CAPACITY. ANYBODY HAVE ANY INFO?THANKS TO DENNIS AND ALL OTHERS FOR THE CONTINUING INFO. ON RADIOS AND VEHICLES, ETC. KEN SAKAMOTO ---------------------------------------------------------------------------------------- Ken, The AM Gen/Government contract is true,but it is limited. Whether or not the government scraps them I don't know,but they don't surplus them,yet. I know of a surplus dealer that could build any amount of them from the 20 acres he has of new parts,all stacked over 20ft tall. Others are driving surplus Hummers that have been restored from badly damaged or blown up examples. As part of the purchase contract AM General has with the government,they can not surplus any vehicles for so many years,this is supposedly to protect their retail sales,I don't think it is so far into the future now that agreement should run out. But who can say what will happin at the end of this contract. I/E it was not any defects,or highway unsuitability that got all the M-151's scraped. It was Ford's complaints & lobbying that the surplus sales of the M-151screwed up their retail sales of the Bronco! By the way the Government cost for a new Hummer is about one half that of the same vehicles cost from AM General to the public. Two years ago two Hummers showed up at the Mo. St. Ag. For Surp. Prop. These were in excellent shape & had been shipped here from Germany. The minute I saw them,I put a hold on them for our county,I was told at the time I probably wouldn't get one because there had been a screw up. It seems that four had mistakenly been turned loose in Germany,only these two had been found,& the government wanted them back. The State would not give them back do to the $2K cost of shipping them here. Much legal fighting was to take place over the next year,but to make the story short,the State got their $2K back & the government their Hummers. As to there value as an emergency vehicle, there is a company that sells fire trucks & other assorted emergency vehicles,all based on the Hummer,needless to say,they cost big bucks! Don't know what kind of carry capacity you need,but a hummer will hold the standard communications shelters that are used in full sized pickup trucks. If anybody knows when this contract it do to run out,let us know,I'd like to see what happens! Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN STARKS ELECTRONICS,wholesale supplier of used communications equipment. *********************************************** SEM-52A,SOME HELP IN PROGRESS. As some of you may know,we have several members that don't live around here. Some in fact aren't even in the U.S. One of these members is Chris who's home ported in Germany. He's consented to do some hunting for a couple of us that own SEM-52's. If there are any others in the group that need particulars for this radio, I suggest we pool them all together & let Chris attack them all at once. Already we have in request for; compatible mic connectors handsets Manuals(english preferred) surplus channel boards If you too have some needs for the above,or any others let me know. A little about the SEM-52; Fair Radio is now selling them for an uncharacteristic $125.00,complete with accessories. The original origin of these radios is unknown,however the U.S. government surplused over a thousand of them last year,& this is most likely where Fair Radio got theirs. The ones in my collection were obtained before Fair got & marketed theirs,& they came here as war trophies from Desert Storm where they had been removed from a Russian/Iraqi Tank. Two questions come to me as to how the U.S. governments came by them. #1,were these radios confiscated stocks of Iraqi war materials? #2,had they been purchased to supplement low availability of U.S. tactical hand helds. If the above true,for who? The U.S. military or to be supplied to one of our allies? In other words,Why did the U.S. government have them? Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN STARKS ELECTRONICS,wholesale supplier of used communications equipment. *********************************************** SEM-52A DATA; by Alan Tasker The stages of the SEM 52-A are varacter
tuned. The little resistor divider on each crystal board tunes the radio
properly by supplying the proper tuning voltage to the varacters. Evidently,
there is a voltage multiplier inside the radio producing 22 Volts, and
this is applied to the top of the divider. For 55.5 MHz, my divider produces
14.5 Volts. For the other frequency (40 something), the voltage is 2.75
Volts (these were measured in my unit). Crystal frequency is Fout + 20
MHz. I do not know if series or parallel, and if parallel, how many pF
load? These were made by Standard Elektrik Lorenz AG, Stuttgart. If any
of us acquire even a schematic, I'm sure we all would like a copy. Similarly,
a source of mike connectors and crystal boards, and better crystal information.
Hey, how about a SEM users group, or should I say a "trying to get going
with the SEM" group???? Alan THE GERMAN SEM-52; By Alan Tasker OVERVIEW The SEM 52-A is a cute, small, 6 channel, low power (300 mW) Military portable of German build (SEL) that comes with an awkward looking (my opinion) head piece containing a tiny speaker and a bone conduction microphone. It runs from 6 ea penlight cells, and has a spare battery pack in its shoulder worn carry case (tape antenna also included). It is available from a couple of renowned surplus dealers. Nobody has come up with any documentation yet, so it takes some fitzing and futzing to try to figure things out. Jane's states that it is a narrow band FM unit, so you're not going to get loud audio when it transmits if you want to re crystal it to use with US mil gear. However, wideband audio is received pretty well in the un squelched mode (EIN). One thing to note is that in the squelched mode (RSP), the receiver is pulsed on for 50 ms every 250 ms (battery saving). If you don't know this, some measurements do not make sense. It usually comes set up with two channels, 47.8 and 55.5 MHz. The crystals are Fch+20 MHz, and they are attached to their own special element board containing the crystal, a cap (27-36 pF), and a voltage divider (two resistors). The crystals are supposedly parallel resonant, 27 pF load in an HC45 holder, but don't quote me. Send the one you are replacing to your crystal vendor so he can determine how to make yours at the new frequency. Nobody knows where there are more of these "element boards," so coming up on more than two channels is going to be very difficult. MODELS You see both SEM 52 and SEM 52-A mentioned. I believe they are all SEM 52-A units. Some of the packing shows SEM 52 even though there is a SEM 52-A inside. Also, Jane's mentions several other versions of the SEM 52 with more channels or different frequency bands. These models have a different letter after the "52." If anyone has seen a nameplate showing a straight SEM-52 without the A, please let me know. HANDSET CONVERSION Kim Campbell was nice enough to send me Mark Gluch's H-250 conversion. I wondered if there wasn't an easier way if you wanted to give up on both the side tone and the 150 Hz CTCSS function (my next project is to put a CTCSS board internal to the unit). There is an easier way, so now I have to get some of the male connectors that interface to the H-250 handset. Anyway, the following info is about the SEM 52 audio connector. Pin "A" is closest to the red dot or line. Progression is clockwise from the top of the unit connector. The first color is the wire color inside the PTT box, (while the second color is the color inside the unit). BE CAREFUL...your colors may vary...Mark and I have one wire a different color. "G" is the center pin. A magnifying glass helps. A, Ear piece, yellow, (green) B, Ear piece, white, (blue) C, Mike hot, center of the shielded wire in both cases(could be red, white, or???). D, PTT, green, (white) E, ?, ?, (yellow) F, +9 V for bone condition mike, brown, (red) G, Mike low, shield in both cases G, PTT return, gray, (shield) The surprise is two wires for the ear piece. There has to be an ohmic connection between yellow and white or the audio goes away. In addition, the DC level is up at 9 V. So, here is what you do. H-250 common (A) to SEM shield, pin G H-250 microphone (D) to pin C H-250 PTT (C) to green pin D 1 k Ohm resistor between yellow and white, A and B 4.7 uF cap (10 V ok, but 15 V better), plus to white, B Other side of cap (-) to H-250 ear piece (B). INNARDS If you take both covers off (metric bolts), here is what you see. Let's define the "up" as the side where we can view the body of the on/off switch and the volume control. There are several shielded items on this side. My experience/assumptions are as follows. L16/17/18 is a input/output band pass filter. The red coated assembly is the mic amp. L1/2/3/5 is an FM modulated 20 MHz oscillator. The tiny bare assembly is a doubly balanced mixer. L6/7/C21/14 is mixer post filtering. C41/L9/C44 is the final power stage(s). The shielded entity closest to the battery box is the oscillator for the main frequency determining crystals...the ones on the element boards in the rotary channel selector switch. R1 is a mike amp level control...CCW is max. R37 adjusts the output power level. The SEM 52 is VVC (voltage variable capacitor) tuned. There is a DC-to-DC converter assembly that creates about 20 Volts, and that is applied to the high end of the voltage divider on the crystal element board. The correct divider must be there to tune the radio for that particular crystal frequency (for example, replacing the 55.5 MHz crystal with one for 51 MHz required adding a 33.2 k Ohm resistor from the divider point to ground). This 20 Volts can be adjusted somewhat by the small pot seen almost obscured by the on/off switch body (on the front panel side). This control can be used to optimize the radio's tuning for any one channel, or to balance the tuning for a couple of channels. On the reverse side is one large shielded board. This is the receiver R12 is the squelch control R9 controls max audio level to the volume control (why I don't know). Comments elicited. Alan Tasker, atasker@ix.netcom.com *********************************************** REVISED SEM-52 DATA; ed) The below data is for crystal information, and the values of resistors needed on the xtal board per the frequency of operation. We beleive the xtal to be an overtone type. Peter Berg came up with the following information about the SEM 52-A crystal and VVC tuning. Thank you Peter. Quartz:UM-1 Intermediate frequency:20MHz Operation Freq. +Intermediate Freq.= Quartz Freq. Example: to operate on 51 MHz, 51.00MHz+20.00MHz=71.00MHz Crystal Quartz precision:10ppm C=15pF Resistor divider consists of R1+R2=220K[+/-20K] Operation Freq. R1 R2 51.00 56K 160K 51.10 60K 160K 51.20 62K 160K 51.30 62K 160K 51.50 66K 158K 52.00 75K 145K 53.00 96K 123K 53.90 110K 110K Where R1 and R2 are per the Japanese web sites, http://www.angel.ne.jp/~sgk1sig/sem52a6.gif http://www.angel.ne.jp/~sgk1sig/sem52a7.gif i.e. R1 is the resistor that goes to one of the crystal terminals and to ground, and the other resistor is R2. Alan Tasker *********************************************** TG-5??? Dennis, You give me any idea what a TG-5B telegraph set in quite excellent condition is worth. 73 from Maine Joseph ------------------------------------------------------------------ Joe Depends on wether it is in a leather case or heavy canvas. They may also be dated from at least as early as 1917 to untel around 1946. With the case,& headset would be around $115 to some Key collectors, leather cases a little more as they are usualy prewar. WW-I dates a little more yet. I've seen them at hamfest being scarfed up like a shark feeding for $50.00 in the canvas case less the headset. This all give you any ideas? Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN military-radio-guy@juno.com ----------------------------------------------------------------------------------- Dennis, What was the TG-5(field telegraph) used for in 1946, or whatever,when field telephones in use? Fred ------------------------------------------------------------------------ Fred, For those that don't know, a TG-5 is a very small field telegraph set, about the size of an index cardfile box. At one time I had the same question. However in years past, I've had opportunity to talk with many of the old farts that used them. The TG-5 was used for two reasons, these follow; #1. in a fast moving combat environment, you may have been lucky enough to have only one wire line strung to your location. The TG-5 allowed for use of two(actually three) circuits from a single line.This because it used only one of the two conductors in a phone line against an earth ground. Thus two TG-5's could be used,(one from each conductor) of this single line. A standard field phone would have allowed only one circuit, but yet could still be used on this same line without interferance,from or with the TG-5's. #2. The TG-5 allowed for the transmission of coded messages over the wire. Something that if tried with a field phone,& voice codes is tedious at best(I/E,the now famous Marine Corps, Navajo Code Talkers). It must be understood that until after the Korean war, radio was used primarily as an expedient. This until wire lines could catch up with the front line units, then as a backup for when these lines were cut. Or where wire lines couldn't be strung. Still today it is preferred by the military to use wire lines whenever practical for obvious Comsec reasons. Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN military-radio-guy@juno.com ------------------------------------------------------------------------------------ Yes thanks - this one must be a late WWII and it did not have the = case with it. Folks at the antique shop wanted *** $ 288 *** for it - a bargan as it was reduced from ***=A0$ 388 *** Naturally I passed on it. 73 from Maine Joseph W Pinner **************************************************************** HT-2A???? Dennis: what is a Hallicrafter HT2A? Is it any good? Ken --------------------------------------------------------------------------------------------- Read my article OPS/Series,Village & Hamlet radio system,letter from me to Keith Melton(backmail #30). The HT-2 is a dual band,30-42mc,& 110-135mc AM,single channel,xtal control handheld that uses "D" cell batteries. It is basically a modified HT-1 which had the lowband AM range only. This modification is an outboard unit bolted to the side of the radio for operation on VHF/AM. They are a neat radio to look at, but not of much good for anything other than to look at The Civil aircraft range was added to allow communications with South Korean & Australian Fighter aircraft in South Vietnam. As we know US aircraft had migrated to UHF 15 years prior. I've never been able to document the use of the radio in Vietnam as with the HT-1 & others, but this doesn't mean that it wasn't used there & or elsewhere. Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN military-radio-guy@juno.com ******************************************************************** ÍMetallsuchgerate MSG 75Î So Bill got himself a mine detector. He has neighbor problems,& do to his increasing age thought it would be much easier to use than a probe. William L. Howard LTC Armor USAR (Retd) East German Mine Detector ÍMetallsuchgerate MSG 75Î This was the standard metal detector of the former East German Army. It was made by VEB Funkwerke Kolleda. The instruction manual has a date of 1/1983 which means this set probably entered service during the 1980Ìs. The set consists of the detector unit and search loop as one piece with the headphones hard wired into the detector housing. Three more handles, a plastic search probe for manual searching after an object is located, complete the set. They are packed in a cloth bag in the standard rain pattern camaflouge found on all East German items. Metal holders are provided for the closing straps. The case is carried like a back pack. The set is powered by 3 R 14 batteries (C Cells) and is claimed to last for 120 hours of use. The operating temperature range is -25 deg C to + 55 deg C , storage temperature range is -40 deg C to +60 deg C. The set is claimed to have an orerating radius of 4 meters wide and 6 meters deep on ground and 1.5 meters deep in water. The search head/detector unit is 1.10 meters long, 0.23 meters wide. The headset cord is 2.3 meters. There are two controls on the set, A 1 is the off/on switch and A 2 is for fine tuning. The set uses two oscillators. Oscillator No 1 is a Colpitts Oscillator and Oscillator No 2 is a Clapp oscillator. All components are mounted on two printed circuit boards. The instruction manual shows 27 capacitors, 36 resistors and 21 solid state components. The manual had a misprint and they forgot to show C 1 through C 14, otherwise the value of each component was given. The set came with an English translation of everything but the principle of operation. Anyone attempting to work on this set would probably need this section translated. Apparent weakness of this set: It is made from aluminum and brass strips and is not as strong as it could be. It can be damaged by rough handling. The search head is a loop which is held together by a plastic bushing which is easily broken by rough handling. The carrying case is not as sturdy as American canvas bags or nylon bags. I have not as yet had a chance to check it out for operation. There may be some problems in the circuit and it may not perform as well as it is claimed to. ------------------------------------------------------------------------------------ I managed to get the set in operaton. It is adequate but would prefer something from Radio Shack or elsewhere. William L. Howard LTC Armor USAR(Retd) East German Mine Detector ÍMetallsuchgerate MSG 75Î REVISED This was the standard metal detector of the former East German Army. It was made by VEB Funkwerke Kolleda. The instruction manual has a date of 1/1983 which means this set probably entered service during the 1980Ìs. The set consists of the detector unit and search loop as one piece with the headphones hard wired into the detector housing. Three more handles, a plastic search probe for manual searching after an object is located, complete the set. They are packed in a cloth bag in the standard rain pattern camaflouge found on all East German items. Metal holders are provided for the closing straps. The case is carried like a back pack. The set is powered by 3 R 14 batteries (C Cells) and is claimed to last for 120 hours of use. The operating temperature range is -25 deg C to + 55 deg C , storage temperature range is -40 deg C to +60 deg C. The set is claimed to have an operating radius of 4 meters wide and 6 meters deep on ground and 1.5 meters deep in water. The search head/detector unit is 1.10 meters long, 0.23 meters wide. The headset cord is 2.3 meters. There are two controls on the set, A 1 is the off/on switch and A 2 is for fine tuning. The set uses two oscillators. Oscillator No 1 is a Colpitts Oscillator and Oscillator No 2 is a Clapp oscillator. All components are mounted on two printed circuit boards. The instruction manual shows 27 capacitors, 36 resistors and 21 solid state components. The manual had a misprint and they forgot to show C 1 through C 14, otherwise the value of each component was given. The set came with an English translation of everything but the principle of operation. Anyone attempting to work on this set would probably need this section translated. Apparent weakness of this set: It is made from aluminum and brass strips and is not as strong as it could be. It can be damaged by rough handling. The search head is a loop which is held together by a plastic bushing which is easily broken by rough handling. The carrying case is not as sturdy as American canvas bags or nylon bags. I have had a chance to check it out for operation. The C cells went in with out problem but it was difficult to screw the cap back on. It would be difficult to do in cold weather or poor weather. The headset does not have any rubber cups and the sound was very hard to hear. This inside in a totally quiet house. Under combat conditions it would be very difficult to hear. The set required constant re-tuning as temperature and conditions changed.. It was difficult to detect small metal objests. A small tool kit with a soldering iron, wrench and pliers was picked up ata distance of about 1 foot. Would probably be more effective with a land mine in the ground. By comparison, the Soviet IMP mine detector which I first tested in 1968 was easier to work with and had greater volume through the headphones.. It is however better than most of the WW II era mine detectors and is fully transistorized. THE WILLIAM L. HOWARD ORDNANCE TECHNICAL INTELLIGENCE MUSEUM e-mail wlhoward@gte.net Telephone AC 813 585-7756 ******************************************************* MAGIC EYE TUBES; THE EM84/6FG6 INDICATOR TUBE by JOHN MACKESY VK3XAO Most of us will have at least a nodding acquaintance with the `Magic Eye' tube - a device properly termed an `electron ray tube'. `Magic Eyes', most commonly the sharp-cutoff 2E5, 6E5 and their remote-cutoff counterpart, the 6U5/6G5, were widely used from the mid-'30s to the '50s. Apart from their tuning indicator applications, they were also used in test and measurement equipment, e.g. L-C-R bridges, and as level indicators in tape recorders. Indicator tubes were rarely used in military equipment, two notable exceptions being the SCR274N/ARC-5 Command transmitters and the RAF R1155. The 6-pin base 2E5, 6E5, 6U5/6G5 and their octal-based relatives the 1629 (12V fil.), Y63 and EM34 (just to confuse things, 6U5/6G5s also exist in octal base!) all shared the same architecture. This consisted of a triode amplifier section and an internal fluorescent `target' viewed through the end of the tube. The target phosphor glows green when excited, the fan-shaped display occupying a 100 degree sector of the circular target. The control electrode (which is mounted between the cathode and target) is connected to the triode section, from which it receives its potential. When the control electrode is less positive than the target, it repels electrons from that sector to produce a shadow on the target behind it. The size of the shadow increases as the potential difference between the target and the control electrode increases. At zero grid voltage, the `fan' is open; as the grid becomes more negative (AVC voltage increasing) it closes. On a 6E5 this occurs at about -8V, on a 6U5 at about -22V. Although useful and deservedly popular for tuning indication, this type of display has somewhat limited resolution. Then again, from a purely stylistic point of view, the large permanently glowing area of the tube adds a certain aura to an otherwise undistinguished radio dial. Enter the EM84/6FG6. Although conceptually similar to the *E5, 6U5 etc, structurally it's radically different. 1. The luminous target phosphor is deposited on the inside of the envelope (like a CRT). 2. The display is viewed through the side of the tube, not the end. 3. A standard Noval envelope is used. The EM84/6FG6 display pattern is very different to the more traditional types, and is probably best described as looking like a pair of greenish curtains which open and close in response to the grid voltage. The target phosphor is deposited on the side of the envelope, and is 39 mm long by 10 mm wide. At zero grid volts the shadow is approx. 21 mm long, the `curtains' closing completely at about -22V. Weak signal sensitivity of the indicator is enhanced by a variable-mu characteristic; the shadow length will change about 6 mm between 0 to -2 grid volts. Although we tend to think of indicator tubes in the radio context (some of us, anyway) the EM84/6FG6 saw wide use in the burgeoning home tape-recorder market of the '50s. In this application, the high resolution display made it a useful level indicator. Whither the EM84/6FG6 today? Although a useful and attractive device, its late-'50s origins put it at the end of the vacuum-tube radio era. Consequently, it was not as widely used as the *E5/U5 tubes, and can be rather hard to find. A good source is derelict '50s tape recorders - these are often available very cheaply at swap-meets and garage sales. Using the EM84/6FG6 The EM84/6FG6 may be operated in any position. To me, the display seems more "logical" when viewed horizontally, but this is a very personal choice, and is based on application as a tuning indicator. When used in pairs as stereo power indicators, vertical mounting seems to have a certain following. Power consumption is very low, typical of this class of tubes, which means it can usually be added on to existing equipment without any problems. Base connections: Pin #1 triode grid Pin #2 internal connection Pin #3 cathode Pin #4 filament Pin #5 filament Pin #6 fluorescent target Pin #7 ray-control electrode Pin #8 internal connection Pin #9 triode plate According to the "Brimar Radio Valve and Teletube Manual (No. 7) "In normal use, the Ray-control Electrode (pin 7) is connected to the triode plate (pin 9)" The following data was taken from RCA Receiving Tube Manual, Technical Series RC-22, published 7-63 by Radio Corporation of America, Electronics Components And Devices, Harrison, N.J.) EM84/6FG6 DATA Ray-Control Electrode Voltage: Without current flowing through series triode-plate resistor: 550V max With current flowing through series triode-plate resistor: 300V max Fluorescent-Target Voltage: Without current flowing through series triode-plate resistor: 550V max With current flowing through series triode-plate resistor: 300V max/150V min Cathode current:: 3 mA max Triode-Plate Dissipation: 0.5 W max Filament: 6.3V at .27A Typical Operating Conditions Triode Plate Supply Volts: 250 Triode Plate Resistance: 1 Meg Series Triode Plate Resistor: 470K Triode Grid Supply volts: -22 Triode Grid Resistor: 3 Meg Triode Plate mA at 0 Grid Volts: .45 mA Triode Plate mA at -22 Grid Volts: .06 mA Fluorescent Target volts : 250 Fluorescent Target Current at 0 Grid Volts: 1.1 mA Fluorescent Target Current at -22 Grid Volts: 1.6 mA Other indicator tubes (by special request): One type of indicator tube made the transition into the digital age - the "Nixie Tube". (Nixie is a trademark of the Burroughs Corp.) These enjoyed a brief vogue in the late '60s/early '70s, being widely used on test equipment, up-market receivers and (wait for it!) - cash registers. The Nixie tube is a device which gives an image of the numbers 0-9 (usually). It's basically a common anode tube, with 9 cathodes, each in the shape of the numbers 0-9. A voltage of about +160 is applied to the anode. The tube contains a small amount of neon; when a cathode is connected (via suitable switching circuitry) to ground, an orange glow forms around it. The display may be viewed through the end or the side of the tube, depending on the type. A filter is often fitted to adjust the display colour. On a personal note, I'd always wanted to own a piece of gear using Nixies. When I was offered an HP 312A Wave Analyzer (really a very good 0-18 Mhz receiver, AM, CW, USB & LSB modes) which has 7 Nixies to give a frequency resolution down to 10 Hz, I jumped at it. It works beautifully, and the display is a great conversation starter. Although Nixies have a long life, it's becoming very difficult to find replacements. If anyone out there knows of a source of Burroughs B5991 tubes, I'd really like to hear from you. The (later) 312B uses a standard 7-segment LED display. Note: "Suitable switching circuitry" can be discrete devices or the TTL 7441 References: RCA Receiving Tube Manual RC-22 (1963). Mullard Valve Tube and Semiconductor Guide (undated). BRIMAR Radio Valve & Teletube Manual No.7 (undated). `70 Years of Radio Tubes and Valves', John W. Stokes, 1982. (This is an exceptionally good read, and deserves an honored place on every tube enthusiasts bookshelf). ------------------------------------------------------------------------------------------- Ed) John, when you told me of your "Magic Eye" tube article, I had thought you might forget those sideways mounted rectangular ones. But I see you've not left anything out, I'm impressed. My youth was spent as a radio & TV tech(early 70's, 14 years old), & I just loved these things. Even though I'm profusely color blind & can only see them in a dimly lit room. Their demise did not really come until the late 60's/early 70's for TV's, & higher power quality stereos this because those units still had horizontal output tubes(for the TV's), or high/mid power audio output tubes(for stereos), and some public address, & gitear type amps utilized them even longer. I think it safe to say that the only real thing that killed them was the lack of an existing power source in the equipment in question, I/E like you say, no more tubes/no more Magic Eye's. I still have some excellent test equipment using them, & they are never shut off. One last comment, in over 25 years of service work, I don't think I've ever seen a bad one. Dennis *********************************************** The preceding was a product of the"Military Collector Group Post", an international email magazine dedicated to the preservation of history and the equipment that made it. Unlimited circulation of this material is authorized so long as the proper credits to the original authors, and publisher or this group are included. For more information conserning this group contact Dennis Starks at, military-radio-guy@juno.com A list of selected articles of interest to members can be seen at: http://www.softcom.net/users/buzz/backmail.html *********************************************** |
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