[GreenKeys] TT-7/FG Restoration

Mon Apr 26 18:54:23 EDT 2021

Hey, 

The manual perforator (not the reperf, which punches mechanically) needs about 250 mA 
at 120VDC to punch tape, so even a 60mA limited loop supply isn't nearly enough. 

A good substitute for the original CVT + thyratron power supples (REC-30 and the like) 
is a modern switching supply - I got this one: 

https://www.aliexpress.com/item/1005002400089527.html 

Works fine, pretty cheap, has a fan that only comes on under load (and isn't that loud.)
It's more than sufficient for punching tape from the keyboard and running a couple of loops 
at once. 

The original thyratron power unit is really fun to watch while it's running, though!

https://www.youtube.com/watch?v=fxy2Ifo8Xx0

There should be a powered AC outlet on the base for the reperf to let you use the existing
weird plug, i think? I haven't moved mine in ages because it's heavy and has stuff piled
around it. 

As for interfacing - there are a bunch of options. You've probably run into my entry, 
the USB adapter that looks like a USB serial port to the computer and like a teletype
to the loop side.   This has the advantage of being able to either translate ASCII/ITA-2
or to pass through transparently.  https://www.heepy.net/index.php/USB-teletype 
The original run is gone but Jordan made a bunch more and may have some available. 

There's also the approach using the dev-kit version of the CP2102 USB-serial chip, which
can be hacked to support 45 baud using some software you can download from John Nagle's
website. You then need to interface its ttl-level signals to/from 60mA current loop, 
for which he also provides plans.   This requires software on your computer to do all the
character set translation. 

Third, and least expensive, it's possible to make a raspberry pi's built in broadcom UART 
speak 45 baud and have a single-character FIFO which makes it quite usable for talking to
teletypes, though again you still need to interface to the loop.  This approach is similar
to the cp2102 way, in that you need to be running software that can speak ITA-2/Baudot
natively, since there's no translation. I have some notes and schematics for interfacing:

https://www.heepy.net/index.php/Optocouplers_for_teletype_current_loop

(To do this with the raspberry pi, and I've only tried it with first-gen pi boards, you
have to modify the source code for the uart device driver and recompile and reinstall the
kernel. It's not a huge project but it's annoying.)

As far as software to actually talk to the teletypes with, everyone has their own favorite.
There's the old "HeavyMetal" in perl which hasn't been maintained for ages, but still
works for some poeple. There's John Nagle's BaudotRSS which has pretty specific functions.
I've written my own in python as a sort of general purpose framework but haven't really
packaged it up for distribution, though anyone familiar with linux and maybe python would 
have an easy time with it. I think a couple of people other than me are using it. 

eric

On Mon, Apr 26, 2021 at 05:29:58PM -0400, Russell Handorf wrote:
> Howdy do to everyone-
> 
> I've acquired two full kits that are the TT-7/FG versions of the
> teletypes. Manuals, tables, reperfs, perfs, keyboard, printer, and power
> supplies in all. I've started cleaning one of the keyboards and printers
> without problems and have it working again. Motor spins fine, no issues
> seen electrically from there. I was able to get it to talk with itself
> doing a loopback with a 10k 1W resistor and 120VDC 5mA limited power
> supply on that line. While a minor achievement, it certainly feels great
> to have it working. I have some questions, thoughts, concerns,
> observations that I'm hoping to get some advise from ya'll folks as I go
> down this journey.
> 
> The first question/observation I have is:
> I did notice I have to power the tape perforater and character counter
> separately if I want to engage those. From the schematics, it appears
> they are separate from the data loopback line. I'm just double checking
> if anyone has guidance/experience with this observation. To get the
> printer, perforater and character counter to work, I have one circuit
> powering the keyboard/printer via a DC loop, and I have a separate DC
> feed going into 24/25. All in all, "am I doing this right?" is the
> bigger question.
> 
> The second one is I've started working on the re-perforater. The unit I
> have has the 4 pin AC plug, and two phonojacks. I managed to clean it up
> pretty well, but I'm in the process of re-writing the 4 pin AC plug to a
> modern plug. Reading the schematic on how the table is wired, one of
> those looks like its a "floating dead lead." But when I look at the
> base, I believe it's connected into the giant filter that's in the
> bottom of the base. Unfortunately, I cannot find the manual or schematic
> for this part of the kit in the doc's that came with it. Does anyone
> have any experience they can share about how to rewiring it for a modern
> NEMA-5-15 plug?
> 
> Third question relates to the power supply. I have three power supplies
> that came with all the gear; two of the normal big "three grunts to
> lift" back breakers and one that's half the size. Between all of them,
> no tubes. I'm not putting a lot of stock in being able to revive them
> without being able to replace the mercury vapor tubes or neon lamps. I'd
> be interested in knowing where a good part supplier is, but there's an
> additional reason for not taking much interest in repairing them and it
> has to do with their operational safety. Which leads me to the question
> of, what alternative power supplies are folks using these days? Straight
> AC to DC 120V with smoothing caps and the like? Boost converters?
> 
> The last question I have has to do with some fun with the machines. Yup,
> I'm looking to plug them into a raspberrypi and then going into the
> wilds of getting them onto the Internet one way or another. I've seen a
> couple of schematics, gizmo's and gadgets that folks have made. I don't
> think there is anything readily "in stock", but I am curious as to what
> everyone has made a decision on using. Part of me wants to spend some
> time trying to make a modification to a board I saw that uses a boost
> circuit. But before I go re-inventing a wheel, I'd like to know what
> works, what hasn't, and noodle on it a bit more.
> 
> Thank you for your time in reading this message. I'm extremely excited
> to be working on these machines and getting them going again.
> 
> Cheers
> 
> Russ
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