LGP-30 Memory Drum Update

Klemens Krause krause at informatik.uni-stuttgart.de
Thu Jan 5 03:44:07 CST 2017

On Wed, 4 Jan 2017, Cory Heisterkamp wrote:

> On Jan 4, 2017, at 1:02 PM, allison wrote:
>> On 1/4/17 1:06 PM, Jon Elson wrote:

>>> Previous messages suggested the LGP-30 drum was plated with nickel.

Nope. I ever wrote about iron oxide.

> I'm far from an expert, but it certainly looks like an oxide coating
> to me. I'm reminded of the folklore when IBM was developing the RAMAC

Yes, I agree.
> In that case it was easy to apply...just spin up the disc and pour!
Good idea, this should work with the drum too.

> There are a couple of 1" long spots where the coating was scraped away and the heads relocated. Given what I've read about the Control Data badged LGP-30's, this was likely a refurb sold in the 60's. The replacement heads certainly support that. Below are some pics of my drum; the tonewheel clock generator can be seen at the far right. The groove just to the left of that leaving a single band in the mag material is too perfect to be a goof, but at the 0.4" head offset spacing, is too narrow to contain more than one track.  -C
> http://www.radar58.com/temp/drum.jpg
> http://www.radar58.com/temp/drum2.jpg

>From the fotos your drum looks better than our working one, with
the exception of the large engraving on the right side. Especially
the left part, were the registers are located looks very good.
On our drum are also some dark traces without showing the Al of
the drum.
I can't see the 1" long spots you're speaking from. How much is
"a couple"?
In your place I would try to revive the drum track by track:
Looking for the registers, find out if the timing tracks S1 to S3
are ok, then looking for tracks 0 to 3 in which the loader,
program 10.4 sits, then track 63, which is used for booting the
loader. Even if you have only some more tracks you can run simple
hand coded programs on your machine. Just think at a KIM-1 single
board computer with 256 bytes of RAM: People had fun with it! :-)

Cleaning the originally coated drum? I'm not sure how to do this.
We clean our RK05 disks in a very robust way: with cheap burning
spirit and paper towels. They have similar technology: Al-base
with iron oxide coating. We rubbed away thick black traces from
occasional head crashes and we never removed the oxide coating
with this torture. In every case the disks were 100% error free
after this. But in this case the risk ist low: the disks had errors
and if we ever would have washed away the oxide coating, we have
enough other disks to experiment with other solvents.
The LGP-30 drum is much more singular, so we never tried to clean
the surface to avoid the risk of cleaning away the coating.


(p.s.: got the book, an interesting lecture)


klemens krause
Stuttgarter KompetenzZentrum fyr Minimal- & Retrocomputing.

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