Source for DEC TC01 (and similar) bulbs?

Josh Dersch derschjo at
Sat Dec 4 22:24:38 CST 2021

Anyone sitting on a pile of these or know where to find some?  These were
originally Dialco 507-3917 or Drake 11-507 based on what was installed in
mine.  24V, 40mA, white.

A total of 23 bulbs were dead on my TC01's panel.  I've installed a pile of
electrically/physically compatible bulbs that I happened to have, but
they're yellow/orange and have a different visual design (the yellow lens
sticks out 1/8" or so, whereas the orginals were flush).  I'm honestly fine
with using them but it'd be nice to have something that looks original.

And a small progress update:  Found that the IOT decode for READ STATUS B
wasn't working, which is done on the W103 decoder at E/F19.  With that
resolved the diagnostics are behaving much more rationally.  This took me
much too long to trace down, but I learned a lot about how the controller
works and found a fun (but ultimately harmless) bug in the Basic Exerciser
diagnostic that threw me off for a couple of days...

The Search Scope loop diagnostic shows block numbers going by in both
directions so a lot of the drive and controller are working, but there's
some glitchiness in bits 2, 5, 8, and 11 of the data so I need to trace
that down; I hope it's not the tape head.

- Josh

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