Another update:

1. I unexpectedly acquired a Model 33 RO yesterday, and it has a good SMD board as far as I can tell.

image.png

2. On my bad SMD board, I tried replacing the transistor with a fairly regular PNP transistor. I had, it turns out, a leftover MPSA56, which is a PNP transistor that happens to support slightly higher voltage and current, while being in a small TO-92 plastic package. This is probably overkill, but that's what I had. I soldered it in, and the selection magnet appears to work! I don't want to prematurely recommend this transistor in particular over another, but I suspect that this board is not very sensitive to the model of transistor used.

image.png

-Erik

On Tue, Jul 29, 2025 at 6:26 PM Erik Bruchez <erik@bruchez.org> wrote:
Terrific photography!  And an amazing project.  That TTY cleaned up really nicely.

Well done!

Thank you, Paul! There is still a lot of work to be done :)