Ok this is very good information. I just wonder if there is any hope of converting this to 8 or 5 bit considering it seems to be the version that has what it needs to do that. Are the parts available? Is it hard to do? If not, I probably won't bother with it.

Bob R suggested I could use it with a 12 bit machine and write out one word two 6-bit bytes at a time. I do actually have a PDP-8/E and I'm pretty sure that is how they did it. But the readers I have, i dont think it has the index hole in an advanced position so it might not work ultimately.

From: W2HX <[email protected]> -- Saturday, March 29, 2025 11:26 AM
> Looks like 7 punches. Does this mean it is a 6-bit (6 data holes, 1 index)?

Your photos show the spacer that allows an old-style narrow punch block in a newer machine that could hold an 8-bit punch block, and
they show 7 punches, for 6 bit data plus sprocket hole, and
one of the photos, taken from a diagonal, shows that the middle pin is not spaced the same as the others -- indicating that the punch block has an advanced feed hole.

That means you have punch block part number 135177, 6 channel with advanced feed hole. The 6-channel tape with advanced feed hole seems to have been a standard in the typesetting industry and nowhere else.

Also, the presence of the spacer means that this machine can hold a newer punch block. The 8-bit blocks designed for this wider framework could be adjusted to hold several different tape widths. Some all the way down to 5-bit tape. (You can tell that they're adjustable because they have so many screw holes for the guide that rides the left side of the tape. See photo below.)
-- https://homepage.cs.uiowa.edu/~jones/pdp8/UI-8/2025/03/20-BRPEblocksSide.jpg

The above photo also shows the spacer next to the 6-bit block with advanced feed hole.

Doug Jones