20ma for an ASR-33 is easy. You're just driving a transistor, not the selector magnet itself. The ASR-33 has its own magnet driver.
The older teletypes, the Model 14 (1920s) and Model 15 (1930s), take more driving. They need 60mA at 120V DC, because you're operating the selector magnet directly. The usual setup is a 120VDC supply with a 10K 2W resistor in series, switched with an opto-isolator. That is simple and works fine.
I designed and built a driver for the older machines that's powered entirely from a USB port, and converts 5V to 120V.[1] This was a fun electrical engineering project. Had to design an unusual switching power supply. A few other people have built this board, including some from the Computer Museum in Mountain View. That packages up the whole power problem in a nice little box. Requires surface mount soldering, though.
The older teletypes, the Model 14 (1920s) and Model 15 (1930s), take more driving. They need 60mA at 120V DC, because you're operating the selector magnet directly. The usual setup is a 120VDC supply with a 10K 2W resistor in series, switched with an opto-isolator. That is simple and works fine.
I designed and built a driver for the older machines that's powered entirely from a USB port, and converts 5V to 120V.[1] This was a fun electrical engineering project. Had to design an unusual switching power supply. A few other people have built this board, including some from the Computer Museum in Mountain View. That packages up the whole power problem in a nice little box. Requires surface mount soldering, though.
[1] https://github.com/John-Nagle/ttyloopdriver