ASR 33 teletype - tape feed magnet voltage

[ct92404]

Hi all,
I hope this is the right forum. I wasn't sure where to post this question. I'm completely new to teletypes, but I've been really curious about how they work and I've been wanting one for a while. Just recently, I was given an ASR 33. It's in VERY rough condition though! I'm going to try to restore it, but it's going to be a major project and I'll have to work slowly and learn as I go. I've started to clean and free up a few parts, and I think the next step I want to try to work on is to free up the tape advance on the reader. I was wondering if there is a way I can just test the electromagnet on the tape reader and see if I can get the tape feed mechanism to work. (Not the tape punch, just the reader). My plan was to just bypass the rest of the teletype wiring and rig up some kind of temporary power supply and hook it up to the magnet and just see if I can get it to work.

I've downloaded manuals and looked at schematics online, but I haven't been able to see anything specific about the circuit for the tape feed magnet. It shows the magnet, but not what voltage it uses.

 

[djg]

Did you find the schematics. I have some here
https://www.pdp8online.com/pdp8cgi/...+Word&dtype=Document+Sets&submit=Submit+Query

Circuit is on page 6 of LT33, 8 of 36 page or 5 of 19 page.

Supply is full wave rectified AC so around 160 volts. There is a 22 ohm resistor in series with AC so will drop some under load. Yes hazardous not always shielded voltages inside. The coil is the box labeled 100 ohms which should be its DC resistance. Note the 9uF 850 ohms. That allows the full 160V to be across the coil to engage the magnet faster but drops it to 17V as the current increases. The reader feed contact closes to advance the tape then opens.

 

[ct92404]

That is a big help, thank you!

I thought I read somewhere that the power supply for the tape reader was a separate module mounted inside the pedestal (I thought that was weird). Although I haven't taken off the cover on the pedestal yet to look.

 

[ct92404]

...Ok, the schematic on the 36 page manual (Teletypes.pdf) is a definitely a big help and should be easy enough to trace out and check. I see the resistor and capacitor you were talking about on the schematic.

 

[djg]

That is a big help, thank you!

I thought I read somewhere that the power supply for the tape reader was a separate module mounted inside the pedestal (I thought that was weird). Although I haven't taken off the cover on the pedestal yet to look.

There are a lot of variants. I have seen one with stuff in the base but can't remember what it was any more.