Military Collector Group Post

                   Backmail #32

(19 pages) Index: Alternate Power Sources; Mark G's Designs For Portables,& SEM-52 Mark Gluch More Alternate Power Source Discussion,For Portables Some Battery Hints,Vibrator & Balast Troubles,Etc. Power Supplies For Portables & Others,Using Whats Out There. Tube Checker As A Power Supply? More Power Supply Tips,Useing Whats Out There.By Pete McCollum Specs for Typical Business Band Power Supply. Just to Get An Idea Of What Can Be Done With Nich Broline Ralph Has Some Progress Line Power Supplies Avail. Complete Specs. The Ultimate Universal Inverter Transformer? & Typical Radio Power Requirements. by Dennis Starks More Inverter Design Discussion; by Mark Gluch, & Dennis Starks Nick's Inverter Transformer Input; by Nick Broline RE: DC-DC; Ralph Hogan, & Dennis Starks Pete's Inverter Transformer Ideas; Filement types? *******************************************

MARK G's SUPPLIES FOR PORTABLE,& SEM-52 MODS Power Supplies for Military Radios, SEM-52 re-channelization. I've hand built a number of DC to DC power supplies to enable the use of military rigs such as PRC-6, PRC-8-9-10, RT-70, BC-611 and BC-1000 from 12V sources. I have also built 12V to 28V converters to allow the use of 24V rigs in "civil" vehicles. They are capable of 100W continous and 150W peak power. A printed circuit version is in design, as I have had numerous requests for these units. It is a 20 kHz boost converter, and the design has proven to be very "quiet" as far as audible or RF noise is concerned. Details: PRC-6 and BC-611 This supply is a 40 kHz flyback type using a Linear Technologies chip and a ferrite core transformer. The BC-611 version puts out 105 VDC, the PRC-6 version puts out 45 and 90 VDC. Input is 12V. If demand warrants, a BC-611 version that operates off of the filament supply could be built. The thing is packaged in a 1.25x1.5x3.25 diecast minibox. RT-70 I stripped the guts out of one of the PP-xxx vibrator supplies, and replaced the vibrator circuitry with FETS and a PWM control chip. It is possible to do the conversion on either the 12 or 24 volt version of the vibrator supply. I'd like to do a solid state vibrator replacement, but haven't had time to get into it. BC-1000 Based on the controller I designed for the RT-70, I built this supply which drives a filament transformer "backwards". Compared to a high frequency ferrite design, it is rather big and clunky, but can be built with many parts from the junkbox. PRC-8-9-10 This supply puts out 135V and 67.5V from a 12V input. The 1.5 V filament voltage and +/- 6V are supplied from dry cell. I don't have plans to go into the power supply business, I'm mainly interested in collecting and operating mil radios. I'll occasionally trade power supplies for radios, but because it is a hobby activity, my time and therefore output capacity is very limited. The priority project right now is a batch of the 12 to 24V systems, I probably will be tied up with that project the next couple months. SEM-52 Another interesting project I've completed is putting a SEM-52 on 52.525 Mhz, and adapting a H-250 handset to it. I also incorporated side-tone audio, and a 150 Hz tone injector. The circuitry for the H-250 adapter is in a die cast minibox that fits in the pouch. It connects to the radio using the the cable and connector salvaged from the rubber ear-mic thing. The frequency change was done by removing the crystal and tuning divider from the 55.5 mhz channel module, and replacing the crystal and re-tuning. Any 6m freq is possible. I'd like to find a source for the modules, as I haven't had much luck reliably duplicating the module board. I'd also like to find a crystal company that has reasonable prices on custom crystals, as I'd like to put my radio on 51.0. Perhaps if enough folks needed crystals we could get a quantity discount. Mark Gluch *************************************************************

MORE DISCUSSION ON ALTERNATE POWER SOURCES; I recently aquired an A510 manpack used by the Australian army in the 50s and 60s. It had a 90V battery, a 1.5V battery and a -6.5V battery. I had to build an inverter to get it going. Was pleasantly surprised at how easy it was to do, as I don't know a huge amount about switching type power supplies. It just uses a couple of transistors switching DC to the secondary of an off the shelf mains transformer. I put an adjustable voltage refulator at the input and just vary it to get the right volts out. Whats more, I fitted all of this, breadboard circuit, 12V battery and transformer inside the battery box of the rig. No hash or other junk in the rx and it txs just fine. 1 watt out. Have had it on the air and its great fun! Cheers,Steve. >Steve Hill > >39 Banbury St. >Carina. 4152. >Brisbane. Australia. ----------------------------------------------------------------------------

Steve,I've been doing much the same thing as you for years,however I use 88mh toroids instead of filement type transformers,because of the much smaller size & greater efficiency,though I have used the "off the shelf transformers" when efficiency & space limitations where not a problem. My PRC-6,CPRC-26,PRC-10,& BC-611,all run off of internal nicad batteries,with no modifications to the radios at all. While it is not to difficult to design an inverter,to make it small enough to fit in the space provided,along with large enough batteries to provide sufficient operating time is a bitch. Marks designs are state of the art & incorporate newly released,exotic IC's. efficiency levels are in the mid to upper 90's,& size is extremely small. At my insistence he's also working on & perfected at least one solid state replacement for the old vibrators. This in the RT-70/AM-65, which would also work in the R-108-110 among others. These too require no modification to the radio,simply an old dud vibrator for the case & connector. I'm familiar with your A510 & hope to have one in the not to distant future. I think 1 full watt however is pushing the envelope a bit. Is not the radio designed for around 500-700mw? Another very useful item Mark's come up with is a 150 watt class 12 to 24volt inverter(to start with). These will allow the operation of such radios as the PRC-47,VRC-12 family,PRC-70,RT-68 family,& many others from our civilian 12 volt vehicals. One more very big design problem incountered when building alternate power supplies for this old multi-cell & very small equipment. Is how to turn it off & on without modifying the original circuits & still using them. All those that I've built use the original switching to accomplish this,& figuring this part out took more time than building the power supply. In the case of the BC-611,this was a monumental task because of the lack of any real controls. Though I was eventualy able to do it,Mark came up with a novel idea. Some sort of other exotic IC that he likes to use,would turn the radio off & on buy rapidly shaking it three times. Can we guess what the onlookers must be thinking when using this system at a Hamfest or other social event? Dennis ************************************************************

BATTERY HINT. Anybody need some of the snap connectors to make batteries for the PRC-68/126 etc? How about some material to make High voltage batteries to run you BC-611,PRC- 6,CPRC-26 etc? Fair radio has had for several years now a sleeper. They are actually batteries for a PDR- 27,rated at 67.5vdc. They will run a Navy RBZ directly by just placing a foam shim under them. The have the snap connectors need,& can be robbed off them for PROC-68 etc. And the cells can be cut them up to make high voltage batteries for your other toys. hey are BA-314 & sell for $1.25ea,I've bought two cases of them(when they still had a quantity price of $10.00 a case) & have had good luck. If you need th snaps for your PROC-68 it's well worth it for that alone. Dennis *****************************************************************


Tod, I have used small low voltage light bulbs,paralleled with power resistors to sub for balast tubes. This is a teadious trial & error proccedure that requires either a good power resistor suber or junk box full of resistors,also differant size(current rateing) light bulbs are required. It does work well once finished. It might be easiar to just build an LM-317 regulator into an octal tube base,these will adjust down to 1.5 volts,& I've done this many times with my battery powered portables. Best source for balust tubes,vibrators,& thermal relays,is junk power supplies. 1AE4's can be had at Fair Radio,or Antique Radio Supply. Theres not a lot of Amatuer interest(lucky for us) in these types tubes,so they are pretty cheap. Mark Gluch is in the process of designing solid state vibrator replacements,he's finished one design for the RT-70/AM-65. Problem with this is the variaty of the vibrators used,this compounded by the fact that service manuals,& schematics seldom tell us the vibrator type used. Thus you must physicaly remove it from the piece of equipment & read the number off of it. & hopefully remember to write it down. Vibrator coils seldom open,or short. Most often the cause of failure is the contacts burn or stick(slightly welded together). This can many times be fixed by lightly rapping the vibrator on your bench top. Other times you can remove the vibrators cover,& free up the contacts,if this done,clean them up while your in there. Also it is for this reason that a 555 & relay would be a poor sub. Your relay/C-434 problem would most likely be taken care of by Fair Radio if you haven't waited to long. They are preaty good about taking things back. Dennis Starks; ******************************************************************

Power Supplies for Portables,& Others,Useing Whats Out There; #1.Using what is out there; Many of us are interested in at least gettin our stuff operational,others want to use the equipment any way possible, & while still others want everything as per mil spec. Often times we must all make some sacrifices, at least temporarily. Here's the biggest tip I can offer to go with the following,when going to a flea market,never look at that $5.00 piece of junk for what it is, instead look at it for what it can be! See what powers it, take note of the type transformers used in it. Can the connector be robbed? If it's to much for your pocket book,check the dumpster after the flea markets over,you may get it for nothing! A very often overlooked source for excellant & very useful power supplies & misc other junk will come from old land (business band) mobile equipment. Here we have three catagories of equipment that will go for pennies at hamfest & numerous other sources. The first is the base station. It can range from a relatively small desk top model(25- 100 watt class), or a large rack mount one worth several hundred watts. For most of our needs the desk top one will work fine. My first TCS power supply came from an RCA desk top VHF base. It operated the TCS purfectly untill the real thing came along,then continued to serve as a test supply for other projects including a GRC-9,GRC-109,& many others. These type LMR radios normaly are a mobile type provided with a power supply for 110vac operation. These power supplies contain everything needed to operate nerely all 5-50 watt class military radios, very little if any modifications to the circuits well be required. They have numerous supply voltages,T/R switching all kindsa good stuff. The second is the higher powered mobiles(25-100 watts), these will often be the same radio as the desk top base with the exception of the type power supply. They can be used for all the same applications as the desk top variaty except in a mobile environment. To this end I've for many years used the supply from an old GE Master Pro to operate my mobile GRC-9. This not because I didn't have the original,but because I didn't have any room for it in the van. Also it's far more efficiant,& I didn't halfta listen to the dynomotor screem. This was very important because I'm almost completely deaf. The third class is the early portables. Also known as Lunch Boxes, Draggie Talkies, Handie Talkie(by Motorola). Be careful here, though most of these types are extemely usefull, do not go a trash a radio that could itself be a collectors item & neet thing to have around. These types have an output power that range from a few hundred miliwatts,to around 8 watts. Power supplies were available that would operate there miniature & sub-miniature tubes from internal 6 6 & or 12volt nicads(yes they had nicads in the late 50's),external 12vdc,& from AC mains. Also dry batteries were the most common used, but we have no use for these,so be sure to look in the battery box to see whats in there. My PRC-10 is being operated from the solid state 12 volt inverter robbed from an early GE portable, it & the nicads are all contained in the PRC-10's battery box. The 110vac supply for an old Motorola Handie Talkie is used as a test supply also for the PRC-10. Absolutly no modifications are required to either the power supply or the radio,the only thing that needed be done was to make a connector/adapter cable. A higher power version of this same supply should be useful for operarion of GRC-9 class radios. #2,What to look for; GE Progress line desk top bases,& mobiles. These were usualy available in 25watt(single 6146 tube),& 50watt(dual 6146 tubes) class radios. The Base options are obvious, but several things should be looked for in the mobiles. Earliar radios will have vibrator supplies,a single one for the lower powered radios, & dual for the higher. Still earliar variants will have dynomotors. For our purpose we need to stick to the later model(at least vibrator),& solid state(much prefured) types. GE TPL(transistorized Progress Line),these also come in 25 & 50watt variants with the same tube line up. They are a much later & smaller radio with a solid state receiver. Their power supplies can be repackaged into a fairly small size. Best to stick to the higher powerd ones because of the extended duty cycle of your all tube equipment, though all are still usefull if cheep or free. GE portables,the predasisor to the Porta Mobile was a much larger radio with a rather primative apperance. It had a solid state receiver & sub-miniature tube transmitter. Designed for operation from internal "D" cells, it's very small inverter can be used to operate many PRC deferant PRC type equipments. RCA built several types that very similar to the GE Progress Line,& TPL in both design & tube line up. Most of thier supplies will be solid state. Motorola built many,many radios that were suitable to our application. I couldn't possibly try to catalogue them all, so will just point out some special ones & things to look for. Generaly look at the output tubes to get an idea of wether the supply will be capable of sufficiant power for your needs. Nearly all of them had solid state variants that replaced the vibrators in later versions,& these are prefured. Some will be of hybrid design with solid state receivers, these too are very usefull. Some of particular interest are below. Handie Talkies,these came in variants that included 1watt & 8watt,hybrid & all tube types. Power supplies for all the variants are differant, though look identical. Internal 6 volt nicad supplies with provisions for external operation from 12vdc, these are most desirable especialy if from a radio that was mostly tubes. AC supplies were also built for both high & low power models that clipped to the bottom of the radio in the place of the battery box. These can be used without modification to operate many of our military pets. A note of caution, some of these radios are very rare, those that operate with less than one watt,or seem very large in size, do not trash them. If these do have inverter type supplies they will most likely use vibrators anyway. Others can accualy be military PRC's as they were adopted by the the US military at least as the PRC-59,& PRC-61 several others are also known to exist. Don't trash these either! MOCOM-30,this is a 10 watt class radio with a solid state receiver & tube type transmitter. It's inverter supply can be re-package into a very small size. A freind used one to operate his grid dip osc,& mounted it internaly. It works from a single "D" cell battery! MOTRACS,these are very common radios. Their supplies are rather complicated,difficult to extract,& repackage. You can still use them though,espicialy as they can usualy be had for the hualing off! We'll thats it. Time to go to work. Yes I do work for a living! Dennis *******************************************************************

Tube Checker As A Power Supply; HI DENNIS THANKS FOR THE WARNING ON ALL THE BOOKS AND MAGAZINES. I HAVE TO CLEAR A PLACE FOR THEM. POWER SUPPLIES. WILL THE POWER SUPPLY FROM AN OLD TUBE TESTER WORK TO RUN A RADIO SUCH AS THE CPRC-10? I GOT ONE AND DON'T WANT TO BUY A BATTERY AND ONLY HAVE IT LAST FOR A LITTLE WHILE. TODD KA0ZDD@JUNO.COM --------- End forwarded message ---------- Tod, I've tried to use the power supplies from tube checkers before. For the most part their Plate & Heater currents are purposely kept very low,thus wouldn't operate radios with multiple tubes. Though the (CPRC-510) doesn't draw much,it's who's guess as to whether it will work. Big problem with battery radios is the low voltage heaters. The power source if not specificaly designed for that voltage & current will pop these tiny heaters in a fraction of a second. The problem is further compounded by the varying resistance of these fragile heaters as they heat up. I/E the surge voltage till the heater lights will usualy destroy them first. This was the purpose for Ballast tubes in nearly all portables operated from alternate power supplies,& why it should never be replaced with a power resistor. Beleive me,you don't want to pop all the heaters in a CPRC-510(I have). No matter what you come up with to power your portable sets,use a simple,cheep,LM-317 in the heater circuit to regulate things. Start out with it at its lowest setting(about 1.2 volts). It well also take up much less room,desepate less heat,& you can get them anywhere. They can also be rangled into regulating high voltages,but I've not done any experimenting with this. The reason I stress this point,is that I have hundreds of portables dating from 1932. In verturaly every case,if they haven't been messed with,they worked when power was applied. If they had been messed with %80 of them had all their heaters opened! So it must be a pretty common ||\\\\> up. Good luck, Dennis P.S. I don't think it helps Bill. ******************************************************************

MORE POWER SUPPLY TIPS,USEING WHATS OUT THERE; Here are a few more power supply tips from Pete. They tend to be a bit more complicated,& for the more technicaly inclined. But do show what's out there for little or nothin,& what can be done with it provided you have a little emagination,& desparation. A note about some very impressive looking high current 12 & 24 volt switching (type regulation used) power supplies. They tend to wreck the performance of receivers such as the R-392. This because you can hear the harmonics of the switching regulator as hash in your receivers front end. I once spent two weeks trying to figure out what was wrong with my R-392. Then hooked up my PRC-47 to find the same problem. Twas the power supply, all that work terrin that R-392 apart for nuthin! Dennis ------------------------------------------------------------------------------------

Here's a couple of other tips related to power supplies: The old tube-based freq counters have "big whoppin'" power supply components in them, since they had so many tubes to run. I used one to make a 60 Hz supply for my R-484/APR-14 (which normally requires 115 VAC 400 Hz). All the DC and filament voltages are piped into the R-484. This allows removal of the rectifier and regulator tubes, so the radio runs cooler. Also, it gets rid of the annoying 400 Hz whine in the audio which you hear when running from a 400 Hz supply. The wiring changes in the R-484 are minimal, and reversible. An HP "Noise Figure Meter" contains a nice power supply with several voltages, including two regulators using 6AS7's. I modified one to produce +150 regulated and +250 regulated (using one of the 6AS7s), and +200-320 variable-regulated (using the other 6AS7), and -150 (at low current), and a couple of amps of 6.3 VAC. There was enough empty space inside, so I bolted a Lambda 28V 7A supply in there also. Used the existing meter to show the variable output voltage. This box will now run all sorts of aircraft stuff, without using the dynos. I picked up a big Klystron power supply for $15, and hacked it up to make a plate supply for a transmitter. It was loaded with high-voltage, high- current power supply components, plus a 4-65A tube (used as a regulator, I think - I took it out). The big transformer put out a higher voltage than I wanted, so I cut it down like this: In the primary circuit of the plate xformer, I put another 18 V xformer to "buck" the line voltage. So, the big xformer sees a line voltage that is reduced by 18V. Changing things in the secondary would have meant wasting a lot of power in the form of heat, and the voltage would 'soar' if there was no load. A LARGE choke at the input of the filter probably would have worked, but I didn't have one... Check out those big, linear supplies that were made for early computer equipment: they typically put out 5V at 20 or 30 A. The high-current winding is center-tapped, so there are two big diodes in there, followed by filters, and a bunch of pass-transistors in the regulator. Add two more big diodes to make a full-wave bridge (this doubles the input to the filter). If the voltage rating of the filter caps is not high enough, wire two of them in series (with bleeder R's). Replace the regulator-control circuitry with a 7812 chip. Now you have a high-current 12V regulated supply. I have two of these in series for 24V at about 30A - just the thing for running my GRC-7! I modified the switching power supply out of a large computer monitor to put out 90 VDC and 6 VDC, to run the receiver portion of an RT-68. Pete ******************************************************************

SPECS FOR TYPICAL BUSINESS BAND POWER SUPPLY,JUST TO GET AN IDEA OF WHAT CAN BE DONE WITH IT. Nick shows use here some of the possibilities found in a typical business band radio power supply. Dennis --------- Begin forwarded message ---------- From: "Broline, Nick (Tracor MS Mail)" To: "" Subject: Specs and Suggestions for GE Prog Line Base Station P.S. Dennis, Here is some data I've picked out for the GE Progress Line power supply Rack Mount version. It was originally directed to a BA net subscriber who was looking for its identity and capability. Actually, it is a pretty versatile package for about any application using firebottles....makes one each bullet-proof universal power supply! _______________________________________________________________________ GE Progress Line Power Supply Model Number EP-4-A HV supply delivered either......... 660 VDC @ 285 ma 425 VDC @ 320 ma 300 VDC @ 150 ma (and other currents for lower power applications.) for the PA high voltage It also delivered 330 VDC @ 110 ma for the exciter B+ 200 VDC @ 30 ma for the oscillator -25 VDC @ 10 ma bias 6.3 VAC @ 12 A for fils 5.8 VDC @ 650 ma for d.c.relay Power Transformer is stamped B-5490007 Connections and color code: Primary: 117 VAC primary black (two wires) Secondary: Start: Red Finish: White 290 VAC Red-Green 350 VAC Red-Yellow 375 VAC Red-Black 545 VAC You can assume that all are rated at about 0.575 A. As you remove the transformer from the assembly, please note that the secondary windings were connected to a terminal strip for the purpose of changing taps to control the output voltage of the power supply. Also please note that the relay is designed to operate from the relay power (nominal 6 VDC) and has the capacity to switch the transformer primary without failures. The low voltage supply: Next biggest xfmr has this number: 7487265-2 And has the following connections: Black(primary) yellow-yellow 18 VAC @ 0.054 A (bias) red-red 270 VAC @ 0.21 A Exciter and oscillator green-green 9 VAC @ 1.85 M Relay supply brown-brown 6.3 VAC @ 12 A Filaments The choke is a 5 H @ 0.300 A d.c. Here are some observations: I note that the power supply is a cap input supply using a choke for filtering, but the input caps are not too large. They use two series 450 VDC caps in each location (two on the input cap , and two on the output) to provide filtering. Each paper insulated cap has a corresponding mate in the capacitor cans, and each is listed as 30 MFD @ 450 VDC. Voltage equalizing resistors (150K) are across each cap to force the voltage division across each series cap to be equal. If one needed a higher voltage supply. say for SSB apps, the voltage output from the highest tap could presumed to be about 545 VAC x 1.414 = 770 VDC with no load, or 681 VDC full load, which is about what is required for a pair of 6146's Using the choke input approach would produce about 545 X 0.9 = 490 VDC under full load (less some small losses), which is good for the plate modulated 6146,s and 807's, etc. For that really high voltage supply, consider using a voltage doubler and get 545 X 2.5 = 1360 VDC under load, which is perhaps a bit low for those 811's. Also note that the smaller transformer is a GREAT transformer for those BA receivers, like the PMR-6's '7's, and '8's, BC-348's, ARR-41's, etc. which like to have 250 VDC or so. The high voltage winding on the smaller will produce, with a choke input filter, 270 X 0.9 = 243 VDC under full load, which is almost perfect! If your power supply was late production the relays should be plug-in. Earlier models are solder-in. Please note that the transformer primary contacts were made of tungsten, and are rated for very large surges and arcs. Schematics are available from me, if anyone has one w/o docs. 73 Nick Broline W5FUA ************************************************************************

Dennis, In reference to your article on using GE MASTR PRO DC-DC switchers for GRC-9 radios (or other rigs with similar needs), I wanted to let you know I have a small quantity of these I removed from GE 60-100W mobile radios. If anyone in the group could use one, I'd take $20 for the power supply w/schematic and $10 for the heavy 12 VDC power cable w/connector + ship or even better TRADE for something neat in return. GE MASTR PRO Model 4EP37A10 EP-37A DC-DC Specs: Input: +13.4 VDC nominal (+/-20%) @ 25A TX, 150 mA to 1A on RX Output: +10 VDC @ 150 mA zenor reg'd -20 VDC @ 90 mA zenor reg'd -45 VDC Bias (also feeds -20 VDC reg) 300 VDC @ 110 mA LO B+ 660-680 VDC @ 280 mA HI B+ The size once removed from the mobile chassis is about 3x3x16-18 inches (real rough guesstimate) As you said before in a previous post, any low VDC can easily come from a cheap 3 terminal LM317 with up to 1.5 A reg output setting voltage from 1.2 V to 37 V (57 V with LM317HV) using only two resistors(transistors not needed for low current ops) or adjustabe using a 240 ohm and 5 K pot. I can gladly help anyone figure it out if they dont have a data book. If more current is required, an external pass transistor may be used. For dropping the B+, series dropping resistors or voltage dividers can be used if one pays attention to R ratings and current load consistency. (Dennis, you may want to add an editors note on how you dropped the 300V for the GRC-9's 120 Vdc 45 mA requirement (No need to,the GRC-9 has it's own internal regulator to provide the receiver B+ from 600vdc while operating with the hand crank gen) If anyone is interested, Ralph WB4TUR email: ******************************************

The Ultimate Universal Inverter Transformer? & Typical Radio Power Requirements. by Dennis Starks Everbodies input is very much needed. My thoughts on what the ultimat universal inverter transformer would be. #1) minimum operational input voltage of 4 volts. #2) with the input voltage of the above, output voltages of; A) 90volts, 60ma B) 45volts, 20ma C) 1.5volts, 1amp, heaters* D) 4.5-6 volt, bias* *)granted these will not be needed in many applications, but we are talking a universal transformer here, & the availablity of these voltages may greatly simplify some power supply designs where the availability of a bias source or power on/off switching etc. without modifieing the radio may be defficault. Higher output voltages will be abtained by increesing the source voltage, via a LM-317 regulator, this will also supply some degree of output voltage regulation. All designs should enclude both input voltage, & heater voltage regulation. Some typical voltage/current requirments for radios of interest, save these because they have been arrived at by experimentation, & many do not exist in printed form elsewhere. The average current drain from the voltage sourse is about 1 amp, you'll need to know this when choosing your battery types & figureing the amount of operational time you'll get from a given battery type. CPRC-26; transmit receive 1.5v/850ma(heaters) 1.5v/550ma(heaters) 45v/8ma 45v/12ma 90v/30ma 90v/3ma -3(bias) --------------------------------------------------------------

PRC-6; transmit receive 1.5v/1amp(heaters) 1.5v/440ma(heaters) 45v/14ma 45v/13ma 90v/28ma -4.6v(bias) ---------------------------------------------------------------

PRC-10; transmit receive 1.5v/900ma(heaters) 1.5v/500ma(heaters) 67.5v/15ma 67.5v/20ma 135v/55ma -6v/(bias & relay) Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN ********************************************************

More Inverter Design Discussion; Dennis: I etched the first board for the 12 to 24 project, will probably build it within a week or so. That thing has sucked up more time than I thought....... Jim K. wants me to do a BC-611 supply next. I'm going to try to do a design that will use two or three D cells, you are right all along in that lower input voltage converters are better as you need few batteries and space is limited. I have two versions in mind- a tiny one (50 mA) thats adjustable 90-105 V with a tap for 1/2 voltage for things like CPRC-26, PRC-6, BC-611, and a bigger 90-135V unit that will do at least 100 mA for things like PRC-10's. A "kit" possibility..... I was over at Jim K's house on Monday, and we fixed my PRC-74. Had bad 6 MHz band, and the antenna tuner meter crapped out. He has a bunch of '74 parts. One way or another, I'm hoping to ttade him out of enough parts to build up a PRC-70 from his scrap heap- It may take a while, and it ain't gonna be pretty, but I think I can be done. Hope your enjoying your new house. I will be in St. Louis on a biz trip Nov 13 and 14, and might be going to the Blues-Red Wings hockey game on Sat the 15. How long of a drive is it to your place from St. Louis? Mark -----------------------------------------------------------------------------------------------------

Mark, About time you woke up. Regard two sizes of inverter supplies, there is no need to build two completely different supplies, one will do the job of all our portable types with an adjustment of the primary voltage source. You can fit four "D" cells in the normal heater battery location on the BC-611, though the plunger will need to be removed(small sacrifice). If a four "D" cell end stacked battery is made for this radio, we will have the added advantage of being able to use the same battery pack in the PRC-6, & two of them in the PRC-10, thus we have further expanded on our attempts at a universal supply. At worst it might be advisable to have the same supply using a common circuit ,board & transformer, but with different windings on the transformer. At all cost the goal should be on the universal nature of the supply, lest it be re-designed for each application(sure as shit don't wanna do that!) I presently only use one design for ALL the portable radios of interest, it is the same for each radio it's installed in, the only difference in each is the DC supply voltage. The only draw back of mine is that it uses 44(for up to 70v) & 88(for up to 135v) mh toroids that can no longer be found with any regularity. Also as this circuit uses the original windings as the secondary, it is impossible to get other voltages like heaters, & bias. The only thing that is hand wound on these are the primary & feedback windings. The completed transformer is only about 1.5"x .5",& the completed supply can be put in a box 1.5 x 1.5 x 2" with ample room left over for such things as bias batteries etc. My point in telling all this is to show that even with a supply of this simple nature, & limited utility,we can still do all the things we need to do, just not as easily. The same battery pack is used in all my radios with the exception of the BC-611. Four "D" cell nicads are included in a cardboard package made from a cereal box turned inside out, & all the flaps glued with a hot glue gun. The cells are arranged so that there are 2 pair/side by side. This setup can be used in the CPRC-26,PRC-6, & 3 packs are used in my PRC-25. Thus I need not carry around a box full of different batteries to operated the various radios in hand. The biggest problem we will be faced with in the case of the BC-611 is power on/off switching without modifieing the radio. In mine, a piece of double sided PC board was used between the battery & the radios normal contact. Between the copper sides of the board is wired a small 5v really that turns on the inverter when the radio is switched on normally. The coil of this really just happened to be of the correct resistance to also act as a ballast resistor for the heaters, so fat chance of repeating this circuit again. P.S. I like the KIT form idea, Build me a PRC-70 while your at it, & I'm a four hour drive from St.Louis. Dennis -----------------------------------------------------------------------------------------------

Dennis: Those 88 mH inductors sure were handy..... I'm gonna work on a 4 D cell supply for the BC-611s that Jim and I have, then see what happens as far as a kit after I have something working. Probably something like a 1x3 PCB with a TO-220 fet hanging off one end will do it size wise. Mark ******************************************************

Nick's Inverter Transformer Input; by Nick Broline Dennis, My favorite power transformer is the tape wound toroid for quick and dirty switching power supplies. As someone correctly pointed out, however, the supply really needs some linear regulation following it for control of filament voltages. The benefit of the tape wound toroid is that it operates with good efficiency, is small, operates at about 1-2 Kc., requires a small number of turns per volt for each winding, is easily wound with your hands, does not require low ESR capacitors in the output filters, does not require big caps either, and it is easy to clean up the EMI. Additionally, the tape wound core inverters have simple switcher circuits (two resistors, two transistors), and are intrinsically short-circuit proof. The problem with the tape-wound circuit is that it does not have the intrinsic capability of delivering regulated output values over a wide input voltage range (like 4.5 to 16 volts) like a high-freq switcher will. I think that it is always prudent to INDEPENDENTLY regulate the filaments of my little ol' radios, so that way I know I'll never get a set of filaments opened up when I'm temporarily overcome with rectal/cranial inversion (which seems to happen more these days). *********************************************

RE: DC-DC >The only draw back of mine >is that it uses 44(for up to 70v) & 88(for up to 135v) mh toroids that >can no longer be found with any regularity. Also as this circuit uses the >original windings as the secondary, it is impossible to get other >voltages like heaters, & bias. The only thing that is hand wound on these >are the primary & feedback windings. The completed transformer is only >about 1.5"x .5",& the completed supply can be put in a box 1.5 x 1.5 x 2" >with ample room left over for such things as bias batteries etc. I've been quite since I stirred up the pot on this issue. Glad to see Mark comment on this. If we all agree, we can have those 44/88 mh torroids duplicated with the extra windings we need. I'm not in love with the exotic switcher chips. Sounds like your TIP xsistor circuit is pretty minimal. ------------------------------------------------------------------------

Ralph, True the TIP-41 circuit does require an absolut minimum of parts, & the exotic IC's that Mark like are sometimes complicated. Mark seems to think that they offer several advantages, also the use of FET's instead of transistors. We shall see. Dennis ******************************************************

Pete's Inverter Transformer Ideas; Filement types? Dennis, Here are some thoughts on inverter transformers: It may actually be needed to use a high-freq osc to keep the size down, but *if* size is not a big problem, then consider this: - Run at 60 to 100 Hz or so, and use a backwards filament xformer. - The low freq should reduce RFI problems a lot. - A variety of xformers are available anywhere. - At 4V in to an inverter, we can approximate this as being 2.8 V RMS. - Using a 6.3 V filament xformer, you would be pretty close to 90 V Peak on the other side. Pete -------------------------------------------------------------------------------------------

Pete, That has already been done & a note is included in a prior post about backwards transformers. The problem is not transformer size, its filtering needed at those low freqs, you need a bunch! Another big disadvantage to these is the single primary winding which will allow only a single output voltage. No problem with such things as a GRC-9 receiver which only needs a single 90 volt supply, but not real handy with others that need multiple voltages. The single voltage output can be supplanted with such things as resistive dividers, but these need be avoided at all cost. There are numerous reasons why. 500-1000cps needs very little filtering, higher freqs even less. Most 60cps transformers will run at much higher freqs. I have several power supplies made that are running between 500 & 1000cps using those little metal sheilded transformers robbed from Jap cordless phones & casset players. These often have multiple primary taps(110/220vac) that will produce 90/45 & 135/67.5 volts output when run backwards. True, suiteable filement transformers are available all over the place, but I'm a tight ass & prefure to get them for nothing. Also surplus vibrator transformers can be used that will operated at around 400cps & up. Marks G has perfected a couple of solid state designs that will effectively replace the old mechanical vibrators used with these transformers. Time has not allowed him to pursue this avenue much further or distribute this info. He seems to be stuck at present on his general purpose 12-24vdc inverter design & gettin it into simi production. A couple years ago I incurraged him to design a solid state multi-vibrator just for use with backwards transformers. One that would have adjusable freq, & would not need feedback(a big problem with transformers of this type). This would provide a simple inverter for the easiar jobs(such as a GRC-9 rec). This project too has been tabled. The current task at hand is to decide on a transformer design that will be as universal as possible so that Ralph H. might have them reproduced in small quantities for the group. Then I suppose there will be some debate on the type circuit used to feed these things. I personally like & use a pair of TIP-41's as a multi-vibrator with feed back supplied by a winding in the transformer. This circuit has proven to be very reliable, simple, & space conserving. A verity of different transistor types can be used. Ralph & Mark both lean toward these late model exotic IC's to perform the job. Though Mark insist that they use a minimum of discreet components, the parts count is still much higher than my TIP-41's. 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, A list of selected articles of interest to members can be seen at:

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