LGP-30 Memory Drum Update

Cory Heisterkamp coryheisterkamp at gmail.com
Wed Jan 4 17:24:50 CST 2017

On Jan 4, 2017, at 1:02 PM, allison wrote:

> On 1/4/17 1:06 PM, Jon Elson wrote:
>> On 01/04/2017 09:03 AM, Klemens Krause wrote:
>>>> We both have analog recordings (from digitizing scopes) and logic analyzer dumps. So concerning the LGP-30, all relevant information about the drum has been saved :-)
>>> We have a second LGP-30 drum in our museum. It is damaged by water.
>>> (large rusted areas, probably from water between heads and drum).
>>> I'm dreaming to wash the brown oxide coating off with a solvent like
>>> acetone, polish the drum and repaint it.
>>> As magnetic paint I would try iron oxide from audio tapes solved in acetone or some other solvent.
>>> Perhaps one could ask an airbrush artist to do this.
>>> Rumours say, that the drums originally also were coated "by hand".
>>> Rewriting the timing tracks should not be impossible with todays
>>> electronics.
>>> There is another guy here in germany, who has a LGP-30 with heavily
>>> corroded drum. That would be certainly interesting for him.
>> Previous messages suggested the LGP-30 drum was plated with nickel. If there are amateur astronomers with a vacuum evaporator, it might be possible to get them to adjust their setup slightly to vacuum evaporate nickel on your drum, after refinishing the base. You'd need a rig to slowly turn the drum while evaporating the nickel. Some other research labs at universities might have the necessary equipment, also - check with the Physics department (or electrical engineering).
>> Jon

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 and finally had success with a magnetic paint mixed up outside of house. In that case it was easy to apply...just spin up the disc and pour!

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


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