I had a Teletype Model 15 and it was my first printer run from an Electronics Australia 2650 system.
It was a fascinating machine.
For some reason I cannot remember, I gave it away. That is something I've mourned over for years.
(My wife says I should just let it go, and of course, she is correct!)

 

I had a Teletype Model 15 and it was my first printer run from an Electronics Australia 2650 system.
It was a fascinating machine.
For some reason I cannot remember, I gave it away. That is something I've mourned over for years.
(My wife says I should just let it go, and of course, she is correct!)

I still have an old Model 15 at my mom's house in Texas that I bought from a Navy salvage sale while based in the Florida Keys. The sight of the massive print carriage lifting up/down during printing I/O from one of my old Z-80 machines was wonderful.

Most of the machines we worked on were the more modern variations like the UGC-6 connected to a KW-7.

https://www.cryptomuseum.com/crypto/usa/kw7/index.htm
The KW-7 was a very cool device to work on with very detailed maintenance procedures.

At the bottom of the machine is the backplane, its wiring and a removable teletype interface (TTY). The bottom can be accessed by removing all screws from the bottom panel and taking it away. This exposes the wiring of the front panel and the wiring of the remote panel connector.
...
The fact that the TTY interface is easily removable, make the machine more service friendly. Note the two cylindrical teleprinter relays at the left. They are the only mechanical parts in the machine and may have to be serviced or replaced at some point. This was done, either by replacing the entire TTY interface, or by opening the individual relays and cleaning its contacts. After the TTY interface is removed, the bottom side of the backplane is exposed, along with its wiring.

Cryptographic algorithm This section discusses the operating principle of the KW-7 and in particular the key generator that drives its cryptographic algorithm. Although the algorithm was initially classified, most of it can be reconstructed from the description in the Repair and Maintenance Instructions Volume I that was declassified in 2009 and published in 2021 [C].​

https://www.cryptomuseum.com/crypto/usa/kw7/files/kw7_kam144b_2.pdf