LGP-30 Memory Drum Update

allison ajp166 at verizon.net
Wed Jan 4 13:02:28 CST 2017

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

Its very likely the plating was done using more conventional bath 

Everything about the LGP-30 screams use of technology that was well known
and not expensive.

It in may ways resembles the PDP-8, linc, and others in the attempt to 
the total hardware to get to minimal computing.  Thing like FlipFlop 
and indirect addressing modes were left out to keep the total tube(and 
logic to a minimum.  A brief look at the manuals and circuits used makes it
clear to keep it small, minimize power, keep it as reliable as possible 
tubes(valves) everything possible was left out.  The 32nd bit missing (gap)
was to likely force a simple case of word end boundary (by oneshot time
out of multiple track coincidence).

 From a make it run again the drum and its heads are only one pair of 
issues to
be examined.  The power supplies (dried out caps!) and coupling or 
capacitor condition as well as general tube status plus the usual 
problems with
wires and connectors including the 400 odd tube sockets.

Keep in mind that generation of machine was not so much logic level as 
presence or absence to be a logical 1 or 0.  So there were few places 
that had
DC static states.  The very next generation of tube and early transistor 
would have registers and static or quasi-static states.

As to the clock track its only issue is that the present electronics 
does not
ever write it only reads it.  So the only issue there is to use the 
existing head or
a data head to write a new track and its only  a matter of having enough 
in the Drum rotation time and insuring the correct gaps if any. That 
would be
trivial hardware to create and keep handy as it can be the very latest tech.


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