[GreenKeys] Model 33 ASR challenge

[Mike Douglas]

 Here is the DEC drawing set for the Model 33 for used with the PDP-9.

https://deramp.com/downloads/mfe_archive/030-Terminals/Teletype/Model%2033/DEC%20Versions/DEC%20ASR33/LT33_print_set.pdf

HP used an external current loop signal to start the reader. Take a look at the schematic link below. HP made an all in-one schematic of the 33 wiring for the HP version of the Model 33. I find it clearer to read/understand than the official Teletype drawing set. Keep in mind, however, there are a few minor differences in this HP version versus an original 33. 

https://deramp.com/downloads/teletype/Model%2033/TTY%20Schematic%20(HP%20Version).jpg

Mike D

     On Monday, June 23, 2025 at 10:18:02 PM CST, Mike Katz <bitwiz at 12bitsbest.com> wrote:  
 
 I have a model 33 ASR that has been modified for RS-232. I am not sure 
exactly what has been done without taking the RS-232 converter out of 
the machine and risking breaking something undocumented.

I have both an Automatic Reader Power Pack and a Manual Reader Power Pack.

The model 33 does not have an automatic reader installed.

I will be connecting the model 33 to a PDP-8 which uses reader 
start/stop control via a custom DEC board installed into the model 33).

I can't just plug the automatic reader power pack because (i believe)to  
the manual reader because the manual reader is missing some wiring and 
circuitry.

Is there anyone out there who has an idea how I can remotely start and 
stop the reader using a currently loop output from the PDP-8?

I already have the PDP-8 working on the PDP-8 without reader control.

Feel free to reply directly to bitwiz at 12bitsbest.com.

Thank you,

              Mike

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