Source for DEC TC01 (and similar) bulbs?

Michael Thompson michael.99.thompson at
Mon Dec 6 09:39:33 CST 2021

On Sun, Dec 5, 2021 at 11:46 PM Josh Dersch <derschjo at> wrote:

> I swapped boards around in the datapath for these bits on the TC01 side
> last night and the problem doesn't move.  On a whim I put my thumb on the
> tape as it passes over the head and it seems to affect the glitchiness of
> the data, at times making it appear to go away entirely.  Doesn't appear to
> be a tape tension problem -- it seems adequate and putting my thumb on the
> supply reel to increase tension a bit does not have the same effect.  This
> would seem to point to the TU55 being the issue, and quite possibly the
> heads.  I haven't had time today to look at the signals coming off the
> heads but I plan to soon.
> Thanks for the help!
> - Josh

I would measure the resistance of the head coils at the relay board
connector. Hopefully they all measure about the same. Figure 2-2 in the
maintenance manual shows how the MARK and DATA tracks are wired, and the
extra connection available for the TIMING track. We found a head on the
PDP-9 where the +D0 connection was open.

Michael Thompson

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