LGP-30 Memory Drum Update

Cory Heisterkamp coryheisterkamp at gmail.com
Tue Jan 3 10:58:07 CST 2017

While waiting for the machine, I decided to investigate the stuck drum.
This unit has 71 read/write heads plus what appears to be an inductive
pickup for the system clock. Upon closer examination I discovered multiple
heads in contact with the drum surface preventing rotation. And in the
process of removing the mounting bars that secure the heads only then did
damage become visible on a couple of tracks (scored oxide under the heads).

What I’m wondering is if anyone is familiar with the setup/adjustment
procedure for getting the heads set correctly. There *might* be a couple of
unused tracks I can relocate heads to, but my thought is that if half a
dozen heads were already in contact, then the rest may be perilously close
as well (swelled drum?). My odds of setting 71 heads perfectly on a 50 year
old worn drum is…well…not great.

For kicks, I tried to use a piece of cheap (=thin) (0.004”) notebook paper
as a feeler gage to see if I could identify the offending heads prior to
support removal. This was a no-go as clearance was too tight. So, is it
true these ride 0.001” off the surface?

I suspect with temp and humidity changes, and given the age, I would be
better off building a solid state drum emulator for the 4KW mem, but
retaining the drum for the clock and possibly the 3 fast registers..if I
can get those (7) heads set correctly.

Any input is welcome.  -C

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