I fully assembled the Model 28 and it looks great. It is working in ‘test’ mode, where the device ignores the signal loop and behaves like a typewriter. It is a bit loud, however.
When I got it, there were foam panels stuck inside the housing, but the foam had thoroughly disintegrated. This foam was there to deaden some of the noise this machine makes when operating. Replacing this isn’t straightforward, since these haven’t been made in decades, and these likely wouldn’t have been a part offered by Teletype in any case.
Cleaning the interior of the housing was quite a chore. The foam was easy to remove as it turned to powder when touched, but the adhesive was some tough stuff. I used citrus oil based GooGone which was effective, but needed significant soak time to soften the adhesive, then quite a bit of scrubbing to remove it. It took a couple of cycles of this to remove most of the old adhesive. To finish, I scrubbed with dawn dish soap to remove the citrus oils, then finished with simple green.
I thought through some ways to replace this material, such as quilting something. It occurred to me that carpet squares may be just the material for this. They are light, somewhat rigid, and I was able to find a decent color approximation.
Making the templates from scratch paper and cutting the carpet is fairly straightforward, but the adhesive on the carpet squares isn’t sufficient for a vertical installation. They do offer a spray adhesive with the carpet squares that seems highly effective. When using it, it sticks quite firmly very quickly so placement has to be accurate. These carpet squares should be durable and dampen the noise of the machine without looking out of place.
Next project is the loop interface to a computer provided by Deramp – Model 15 Interface. It will take quite a bit of assembly, so I don’t anticipate a fast build, but with a signal loop I’ll be able to use this close to its original purpose.
This thing is quite complicated mechanically, and it took a bit of doing to find the manuals, find what manuals applied, how to find things in the manuals, then learn the terminology, and so on. The problem turned out to be a broken part that needed replaced. The broken part was responsible for resetting the keyboard after a key was pressed, so you could press a key once, then manually had to reset the code bars to press a key again.
Doing this required disassembling the major components, then disassembling the ‘signal generator’, which is the assembly attached to the large geared shaft
This assembly has a bunch of tiny parts and I am surprised I didn’t lose anything. Reassembly took quite a bit of fiddling with adjustments, fortunately the manuals run though these and I got a better understanding of what all this stuff does.
While I had it apart, I did disassemble the main drive gears to determine the speed of this machine. The nylon (ivory color) gear in the center is one gear that determines speed, but the part number isn’t visible when assembled. Disassembling this permitted me to pack the roller bearings with grease and find the part number – 195997 found in 573-116-800TC-iss3-7012. The speed of this machine is 100WPM.
Now that it is working mechanically, I can start trying to figure out how to interface this with a computer. 100WPM is not common on amateur radio, so getting this to work directly on the air wont be practical, but I can use it indirectly with fldigi and send text to it as a way to print text. This does get me interested in a machine that I can use directly on the air, maybe a Teletype Model 15 at some point.
Simple Green concentrate and a soft toothbrush cleaned up the Teletype really well. Stubborn oil residue came off with a fingernail or toothpick. There are several springs that probably could come loose with vigorous scrubbing so I was careful to use light pressure. I set these subcomponents in a plastic tub and sprayed and scrubbed for awhile, then rinsed and set them in the sun. There are small spots of rust sheen here and there, but ill very lightly coat surfaces with oil.
Disassembly of the subcomponents was surprisingly easy. Just a small handful of fasteners, two electrical disconnects and the typing unit and base/keyboard unit came out without a fuss. Now that it is clean and I am confident there are no exposed electrical contacts, I can reassemble and test after lubrication according to the manual – Teletype Bulletin 217B
If there was an answer back feature, the music box like drum would be behind the keyboard on the right, the “Here Is” key would be one of the red keys. This model did not come with it which means I’ll have no means of getting an idea of where it was in service.The Typing unit turned out very well.The Keyboard and Base unit dataplateThe felt pads that hold oil all seem in good shape
Before I plug this in, I need to inspect the machine to ensure it won’t be damaged or gummed up as it begins to operate. A helpful person that sells parts for these machines recommended simple green as a gentle degreaser, followed with lubricating according to the manual. Manuals can be found at Teletype Corp. Maintenance, Installation, Operation, and Parts Publications (navy-radio.com) although getting familiar with the terminology will take a bit
The last page it typed with perhaps a news wire
This machine is gummy and dusty, but as far as I can tell there is no mechanical damage or electrical burns on it. Wires all appear intact. The primary motor that gets everything moving spins freely and moves the internals around quite a bit in what I think is correct operation.
Called a range finder in the manual, I thought this set words per minute, but there is a gear that does that somewhere in the machineDataplate for the typing unitTyping unit and maybe the code bar mechanism at the bottom
Looking at the manual, it appears that there were two paper feed mechanisms, and I have the ‘sprocket feed’ type. Modern term seems to be ‘continuous form’ paper, which if the dimensions are the same, appears to be readily available. Its been decades since I have seen this type of paper though. The sprockets are a fascinating mechanism, the teeth retract as they rotate to only be out when needed to pull paper, and retract when they would get in the way of the mechanism. It appears to be working smoothly.
The keys don’t ‘press’ which may be normal if there is no power applied. Nothing appears bent or broken underneath.What should be the communications interface, with a Tip/Ring/Sleeve plugThe tip/ring/sleeve plug ends up on this board, with 5 and 15 being connected as well as chassis ground. These panels are at the bottom cabinet of the machine, above the paper storage and in front of the electrical service unit
I will have quite a bit of cleaning ahead of me as there are many places gummy residue is hiding, but I am fairly optimistic that this is in good shape and will be either working or repairable.
Ill have to interpret what connections 5 and 15 are and that should move me towards understanding the input output of this device. Using some sort of serial connection isn’t possible directly, it requires a fairly stout (likely 60ma) current to drive it.
This is a wall mount machine, but someone in the past made a cart for it. It is a very heavy device.
The AN/PRC-9 sets was disappointing to miss out on, but I did get one item I have been after, a teletype.
Last time I saw a teletype in service was mid 90s, email and other electronic communications made these unnecessary since you could print what you needed and discard the rest without wasting consumables. Like the Remington typewriter I have, these mechanical devices are fascinating and the distinctive sound they make should be nostalgic for anyone visiting the station that worked with teletype when they were in service.
It appears to be in good condition, with no obvious damage, but getting this hooked up to something to drive it will be a challenge. Goal will be getting it cleaned up, operational, and able to type things I send it from a Raspberry Pi using FLRIG and FLDIGI. Actual RTTY seems fairly rare these days but I should be able to send text from any digital mode, or really any text that I want a printed copy of.
Edit – FairRadio ran out of stock before my order, so I wont end up with these. There really aren’t many places that have these either so I may have missed my window. Disappointing but ill keep looking and hopefully get lucky sometime.
Following the SCR300 radio, the Army acquired the PRC-8 (Armor)/9 (Artillery) /10 (Infantry) series of radios. These radios were in service for the 50s and early 60s. I previously have taken an unsalvageable PRC-9 as a housing for a modern radio set, but I got a couple of additional salvageable radios which I intend to make operational mostly as issued. The batteries are no longer made, so I wont be able to use those, but there are some alternative power sources I have found that others have come up with.
Refurbished case housing an Icom 880H modern amateur radio
The PRC-9 that I used gave me a bit of familiarity with the innards and the parts that weren’t corroded I kept. This should give me some spares, a few of the tubes seemed to be in decent shape.
From an amateur radio use perspective, the PRC-10 (38.0 to 54.9 MHz) covers the 6m band and the PRC-9 (27.0 to 38.9 MHz) covers the 10m band. I selected this model because it was the Artillery version, not for its frequency coverage, but it appears that I got lucky, 10m seems more active to me than 6m over the years I have been listening to the amateur bands. The PRC-8 (20.0 to 27.9 MHz) would have been a good selection too, covering the 15m and 12m bands.
I have been wanting a deeper understanding of radio for quite awhile, and this project should do just that. I did work on tuning 12 series radios (the RT-524) in the late 90s full time, but that was just following a script more than understanding fundamentally what I was doing. My basic understanding is that antennas pick up tiny voltage differences and amplify them but the roles of the various components I am not familiar with. Ill just have to start at the beginning, take this in steps, and slog through the math. The math part I am not really enthusiastic about, but I won’t gain an understanding if I skip that part.
I also have a second Transoceanic 3000 that needs repair that I can explore after this project, which should be an interesting comparison of differing receiver designs.
The connector itself is unlikely to be bad unless its damaged, if you are doing a rewire it is likely that this part won’t need replaced, just redone. If you get a replacement you will have to wire it anyway. In my truck the wire insulation was crumbling in places so I am doing a complete rewire, including this assembly.
Use silicone grease and gently nudge the protective rubber shell over the wires. It will take some patience as you don’t want to damage the rubber so it can be reused assuming its still serviceable.
Once cut free, you can tin the solder cups. Lead free solder was not working for me, I had to use lead solder. The cups have to be clean and clear, I heated each cup with iron at highest heat setting and tapped the assembly on the worktable to dump the solder in each cup. I used a torx screwdriver to ream out each cup to have a clean surface as used flux and other junk accumulated in these cups.
Solder cups before cleaning
Before soldering, the wires must be combed and in the correct order or it will tangle up and the protective rubber shell won’t fit over the wires as it should. All the parts should be inline as it will be when it comes together to prevent not being able to get it assembled when complete. Juggling the wire order while also trying to work in the tiny spaces is a challenge. Wiring from the inside of the assembly and working your way to the outside ring helps a bit with the cramped space.
Tin the wire, if using the military type 14 gauge M13486/1-5 wire (Prestolite is the maker of the wire I have), it will take high heat and lead solder to tin this wire. It should have a coating of solder without blobbing, and should fit into the cup on the connector. Flux well and heat the connection, when you feel it drop down into the cup, and is filled with solder, the connection is done. It takes some time and a lot of heat to get the wire to drop in the cup. I used denatured alcohol (sold as alcohol fuel at home depot) and qtips to clean up flux.
Testing completed project, note the rubber shell that still has to slide down to separate the connections where the wire meets the cups, if the wires are not in proper order, it will not come together.
The metal wire tags and stamp set I found at https://www.nationalband.com/wrap-around-tag-m434363-1/ part or style number is M43436/3-1. The 1/8th in stamp size fits on the tag and appears to be what was used on the original. The stamp set is found at https://www.nationalband.com/fasteners-accessories/ as style 1571. The sales rep told me you can wrap these with finger pressure and I didn’t really believe it, but its true, they bend into shape fairly easily, but once on are sturdy. When stamping the numbers I am using a light tap with a light hammer, it does not take much to imprint the numbers on the tag.
Example of a wire tag, circuit 491
The opposite side of this assembly will be Packard rubber shell connectors so the assembly can be serviced later if needed.
One thing I thought when I got this truck, after looking under the dash, was “I hope I never have to mess with the wiring”.
On rare occasions, this truck would act flaky with the electrical systems, headlights wouldn’t turn on or difficult to start, but it was always brief. I did get a three lever switch at one point, but the problems never really occurred that I noticed after this.
After the rebuild, and driving it for a bit, I noticed the service lights were flaky and I didn’t have turn signals. I got it home and discovered a fuse was melting but not blown. I poked around for a bit and decided to stop driving it since something electrical not working right is a great way to start a fire. A good thing I did, since I found what was likely the foundational issue, the main battery cable sheathing had worn through in multiple places and was arcing on the truck somewhere. The wiring in general is about 20-70 years old and probably could benefit from a refresh so I am doing a rewire. There are wiring harnesses out there for sale, but all of them assume a fairly standard M37, which mine is not. Its a 24-12v conversion with some extra items that aren’t on a standard M37, a siren, cab heater, and whoopee light for instance, as well as some engine modifications to the ignition system that make going back to 24v impractical.
Ill post about this project as I complete systems to document my experience.
Finally ready after nearly 2 years of rebuilding. The engine has a lot of power, easily climbing up hills that it struggled with before. The cacophony of odd noises is much less, and the engine oil is as amber as it comes from the container without all the liquified char. The last part I assume won’t last long, but its still jarring to see a military vehicle without liquid carbon as crankcase oil.
For Winter Field Day we setup at Perry State Park, vicinity of Catfish Alley – https://ksoutdoors.com/State-Parks/Locations/Perry/Perry-Gallery/Catfish-Alley-Primitive-Campground
Got the M35a2 serviced at Valley Truck & Trailer – Truck Repair Shop in Valley Falls (business.site) – and they did a fantastic job getting old rubber items such as coolant hoses, belts, and other seals changed just in time to get us in the field. Everything was soggy from ice melting and rain the previous day, so getting fires started was a challenge. The coal stove never got hot enough to light properly but fortunately we had a Mr Heater propane stove that worked very well.
We made a large handful of contacts, but not a huge number, our focus was working out tech issues and showing the people new to amateur radio the basic procedures. Also, we just had a ton of fun just camping and made a relaxing weekend of it. I am very happy with the setup, getting on the air didn’t take much time at all and we didn’t have the problem of hauling heavy items to the tent to operate.
Our setup was an IC7300, with IC7200 in reserve, next go around we will get both radios going one digital and the other voice. Bearcat 996XT to monitor the local activity, and an IC880H for VHF. Antennas were discone and VHF on masts, and Shark hamsticks for HF. The hamsticks perform very well, and we are assuming the massive ground plane of the truck is helping, I really need to test this vs the other antennas I have to see how well they really do in a comparison.
One of the people that joined us brought a photography drone and it took the neat overhead orbital.
