Re: LGP-30 Memory Drum Update
On 1/5/2017 9:49 AM, Pete Lancashire wrote: I would clean all the heads, and the surface with a soft cloth and give it a try. A place I worked, a "soft dry cloth" unless it came out of a package made by Texwipe or their competitors was known as "sand paper", if you were caught using such you were fired on the spot and escorted out the building. Same for paper towels. Just my 2c's -pete I agree 100%. I keep shaking my head in disbelief at these references to paper towels and other dry forms of sandpaper. - J.
Re: LGP-30 Memory Drum Update
Kimwipes ! That's the brand and products I could not remember. Just one thing to add, there are many different types/variations, so be careful. On Jan 5, 2017 7:15 AM, "Paul Koning" wrote: > On Thu, Jan 5, 2017 at 3:44 AM, Klemens Krause < > kra...@informatik.uni-stuttgart.de> wrote: > > > ... > > 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. ... > > 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. > > I've seen an IBM field service tech clean an 1311 pack once (after the > drive blew a gasket and sprayed hydraulic fluid everywhere). He used > Kimwipes soaked in isopropyl alcohol. Since this was in college, I went to > the chemistry department to get high purity (reagent grade) isopropyl > alcohol for this job. > > A solvent sounds good, but I would avoid "burning spirit" or rubbing > alcohol or other grocery store stuff since it probably has all manner of > contaminants in it, some of which may leave crud on the surface. > > paul > > >
Re: LGP-30 Memory Drum Update
>>I would clean all the heads, and the surface with a soft cloth and give it a >>try. A place I worked, a "soft dry cloth" unless it came out of a package made by Texwipe or their competitors was known as "sand paper", if you were caught using such you were fired on the spot and escorted out the building. Same for paper towels. Just my 2c's -pete On Thu, Jan 5, 2017 at 1:41 AM, Christian Corti wrote: > On Wed, 4 Jan 2017, Cory Heisterkamp wrote: >> >> 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 > > > Yes, it is ferric oxide. > >> http://www.radar58.com/temp/drum.jpg >> http://www.radar58.com/temp/drum2.jpg > > > Hmm, your drum doesn't look to bad after all. In your case I would clean all > the heads, and the surface with a soft cloth and give it a try. For basic > testing you only need one data track plus the register and timing tracks. > > Christian >
Re: LGP-30 Memory Drum Update
On Thu, Jan 5, 2017 at 3:44 AM, Klemens Krause < kra...@informatik.uni-stuttgart.de> wrote: > ... > 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. ... > 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. I've seen an IBM field service tech clean an 1311 pack once (after the drive blew a gasket and sprayed hydraulic fluid everywhere). He used Kimwipes soaked in isopropyl alcohol. Since this was in college, I went to the chemistry department to get high purity (reagent grade) isopropyl alcohol for this job. A solvent sounds good, but I would avoid "burning spirit" or rubbing alcohol or other grocery store stuff since it probably has all manner of contaminants in it, some of which may leave crud on the surface. paul
Re: LGP-30 Memory Drum Update
On Thu, Jan 5, 2017 at 3:44 AM, Klemens Krause < kra...@informatik.uni-stuttgart.de> wrote: > >> >> 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. > That is encouraging news. The engraving on the right appears to be machined into the drum as it's much deeper than the oxide finish and completely uniform. I'm not sure what purpose it serves, if any. I've adjusted the 7 heads along the left side as one was just making contact. > I can't see the 1" long spots you're speaking from. How much is > "a couple"? > There's a total of 3 such marks on the drum not visible in the photo, 2 caused at some point in the past as the heads that caused them were relocated from those tracks, and one short scratch caused by me after having removed all but the last head bar assembly and checking for drag. It seems each bar had at least one, if not more, heads in contact with the drum, which I was not expecting. > 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! :-) > I think this is a good idea. I hadn't planned on running anything other than hand coded programs, and having at least several tracks functional will help me in troubleshooting the rest of the machine. I can then transition to a solid state mem later. > > 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. > I used a clean, soft, paper towel without any solvent or liquid and gently ran it from left to right while rotating the drum. This picked up a little fine oxide, but whoever serviced the drum last did an excellent job of sealing it. After they replaced the plastic cover they ran strips of electrical tape (which was still firmly stuck) down both sides. The air filter is also still present on the machine which is a good sign. -C
Re: LGP-30 Memory Drum Update
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. Klemens (p.s.: got the book, an interesting lecture) -- klemens krause Stuttgarter KompetenzZentrum fyr Minimal- & Retrocomputing. http://computermuseum.informatik.uni-stuttgart.de
Re: LGP-30 Memory Drum Update
On Wed, 4 Jan 2017, Cory Heisterkamp wrote: 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 Yes, it is ferric oxide. http://www.radar58.com/temp/drum.jpg http://www.radar58.com/temp/drum2.jpg Hmm, your drum doesn't look to bad after all. In your case I would clean all the heads, and the surface with a soft cloth and give it a try. For basic testing you only need one data track plus the register and timing tracks. Christian
Re: LGP-30 Memory Drum Update
On 01/04/2017 09:56 PM, Jon Elson wrote: > On 01/04/2017 05:24 PM, Cory Heisterkamp wrote: >> >> 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! >> >> >> >> http://www.radar58.com/temp/drum.jpg >> http://www.radar58.com/temp/drum2.jpg > Yup, that looks pretty "oxidey" all right! > > Jon > Based on more than a few drums and disks i've seen its oxide, not plated. I'd also say if the scratches are not deep a little polishing may be the trick. I'D do nothing until it can be run up (remove all dust and gunk) and then look at the output of the heads. Likely you don't have to write clock tracks if there is mechanical (tone wheel). If so that means the clock is created there so its always in sync with drum rotation. That's one less headache. I have a hunch that the data/instruction tracks are not pre-recorded and can be over wrote and replaced at will but there is where the manuals and a thorough understanding of the machine and its logic is needed. IF the data tracks are created by other timing (clock and logic) then erasing a track is safe (check manuals) and then you can write a track with F and 2F and see if it reads out uniformly if it does that head is good and the media under it is. Step and repeat, any that fail or have to many drop outs or other errors need care, relocate first and try again. This is about what old school tricks need to be found out about and relearned. The closest analogy is how to steam and repair a coal fired locomotive. There is hand me down knowledge that will be needed and learned or even regenerated. A very interesting project. Allison
Re: LGP-30 Memory Drum Update
On 01/04/2017 03:50 PM, Paul Koning wrote: >> On Jan 4, 2017, at 2:48 PM, Kyle Owen wrote: >> >> On Wed, Jan 4, 2017 at 12:06 PM, Jon Elson wrote: >>> 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). >> >> Will the desired thickness be enough with sputtering or evaporation? For >> modern hard drives, sure, but my gut instinct is that you'd want a thicker >> coating on the drum. I'd suggest sputtering over evaporation since it will >> probably adhere to the surface better. I'd think nickel electroplating >> would take less time and effort, though. > Electroplating sounds ok, I don't know about procedures. You'd have to be > careful that the electrolyte doesn't damage the drum body. > > Evaporation and sputtering are used to make well controlled thin films, but > there's nothing I can think of that limits how long you continue. A mirror > is coated only to the point that its reflection coefficient reaches the limit > of the metal used, more is not useful. But here you could just keep going > however long you need. > > As for adhering, both should produce good coatings if the substrate is clean. > I remember a test for good evaporative coating technique: coat a test piece, > then try to rip off the coating with scotch tape. It shouldn't be affected > at all by that test. > > There are reasons for using sputtering vs. evaporation, but I don't remember > them. I think the Strong book I cited discusses the subject. Several things. Getting aluminum clean and keeping it so means NO oxygen, it develops a oxide coating really fast. Other metal might be used but your generally limited to non magnetic substrates (aluminum, glass, brass, bronze). Also the thickness of the magnetic media, rate of travel (speed relative to the head), head distance and gap are all interrelated. For heads of that era the gap will be wide, the media thick, and the rate of travel high. Those factors determine bit density (likely very low) and the data rate is really low as the machine is slow. If the drum is scratched then moving heads one gap width right or left should do fine. Plated media doesn't help with this save for its mechanically easier to do. Allison > paul > > >
Re: LGP-30 Memory Drum Update
On 01/04/2017 05:24 PM, Cory Heisterkamp wrote: 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! http://www.radar58.com/temp/drum.jpg http://www.radar58.com/temp/drum2.jpg Yup, that looks pretty "oxidey" all right! Jon
Re: LGP-30 Memory Drum Update
On 1/4/2017 7:56 AM, allison wrote: Sperm oil was a high quality wax/lubricant. Its low viscosity and high resistance to oxidation were its high points. Its likely use was as a plasticize the binder and surface. As far as I know it is illegal to purchase or transfer now. Not to possess. I have the supply my father had because he was a watchmaker. he had bought a lifetime supply in the 40's and it is still 90% there. But I can't transfer it. He used a very small drop in a small dimple holder with a cap over it for about a year. A sharp needle provided all that was placed on watch bearings. I'm sure it would be ideal for this application, but can only agree with Allison about the properties of it now days. thanks Jim
Re: LGP-30 Memory Drum Update
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 http://www.radar58.com/temp/drum.jpg http://www.radar58.com/temp/drum2.jpg
Re: LGP-30 Memory Drum Update
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 electroplating. 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 minimize the total hardware to get to minimal computing. Thing like FlipFlop registers and indirect addressing modes were left out to keep the total tube(and diode) 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 with 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 interstage 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 pulse 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 machines 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 pulses 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. Allison
Re: LGP-30 Memory Drum Update
On Wed, Jan 4, 2017 at 12:30 PM, Chuck Guzis wrote: > On 01/04/2017 11:48 AM, Kyle Owen wrote: > > > Will the desired thickness be enough with sputtering or evaporation? > > For modern hard drives, sure, but my gut instinct is that you'd want > > a thicker coating on the drum. I'd suggest sputtering over > > evaporation since it will probably adhere to the surface better. I'd > > think nickel electroplating would take less time and effort, though. > > > > Heck, I have about 4 L of nickel plating solution as well as an > > anode, if someone wants to give it a shot. > > > Thinking more about this a bit... > > "Modern" aluminum-substrate plated media uses a layer of electroless > nickel, which is then polished, then plated with a layer of electroless > cobalt. I don't know if cobalt can be vacuum-sputtered onto nickel. > > Lubrication layers are often added in the case of Winchester drives. > > I suspect that the LGP30 drum heads require a substantial signal, so > perhaps 5 micron cobalt plating wouldn't work. In any case, the low > recording density might be better realized through a traditional > iron-oxide-in-binder coating. > > I am not a EE, but in a ignorant attempt at of the box thinking. Make a new drum out of AL, glue strips of COTS magnetic tape to it. -- Charles
Re: LGP-30 Memory Drum Update
> On Jan 4, 2017, at 2:48 PM, Kyle Owen wrote: > > On Wed, Jan 4, 2017 at 12:06 PM, Jon Elson wrote: >> >> 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). > > > Will the desired thickness be enough with sputtering or evaporation? For > modern hard drives, sure, but my gut instinct is that you'd want a thicker > coating on the drum. I'd suggest sputtering over evaporation since it will > probably adhere to the surface better. I'd think nickel electroplating > would take less time and effort, though. Electroplating sounds ok, I don't know about procedures. You'd have to be careful that the electrolyte doesn't damage the drum body. Evaporation and sputtering are used to make well controlled thin films, but there's nothing I can think of that limits how long you continue. A mirror is coated only to the point that its reflection coefficient reaches the limit of the metal used, more is not useful. But here you could just keep going however long you need. As for adhering, both should produce good coatings if the substrate is clean. I remember a test for good evaporative coating technique: coat a test piece, then try to rip off the coating with scotch tape. It shouldn't be affected at all by that test. There are reasons for using sputtering vs. evaporation, but I don't remember them. I think the Strong book I cited discusses the subject. paul
Re: LGP-30 Memory Drum Update
On 01/04/2017 11:48 AM, Kyle Owen wrote: > Will the desired thickness be enough with sputtering or evaporation? > For modern hard drives, sure, but my gut instinct is that you'd want > a thicker coating on the drum. I'd suggest sputtering over > evaporation since it will probably adhere to the surface better. I'd > think nickel electroplating would take less time and effort, though. > > Heck, I have about 4 L of nickel plating solution as well as an > anode, if someone wants to give it a shot. Thinking more about this a bit... "Modern" aluminum-substrate plated media uses a layer of electroless nickel, which is then polished, then plated with a layer of electroless cobalt. I don't know if cobalt can be vacuum-sputtered onto nickel. Lubrication layers are often added in the case of Winchester drives. I suspect that the LGP30 drum heads require a substantial signal, so perhaps 5 micron cobalt plating wouldn't work. In any case, the low recording density might be better realized through a traditional iron-oxide-in-binder coating. --Chuck
Re: LGP-30 Memory Drum Update
On Wed, Jan 4, 2017 at 12:06 PM, Jon Elson wrote: > > 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). Will the desired thickness be enough with sputtering or evaporation? For modern hard drives, sure, but my gut instinct is that you'd want a thicker coating on the drum. I'd suggest sputtering over evaporation since it will probably adhere to the surface better. I'd think nickel electroplating would take less time and effort, though. Heck, I have about 4 L of nickel plating solution as well as an anode, if someone wants to give it a shot. Kyle
Re: LGP-30 Memory Drum Update
> On Jan 4, 2017, at 1:06 PM, Jon Elson wrote: > >> ... >> > 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). Nice idea. You'd want to check that the same filament works with nickel. Standard mirror coating is aluminum, using a tungsten filament. Some other metals don't work that way because the molten metal doesn't adhere to tungsten (silver is an example). The procedure, including the filament to use, is described very nicely in "Procedures in Experimental Physics" by John Strong. It was reprinted by Lindsay Publications, now out of business but it might still be available. Great book, also for some other crafts such as glass working (useful for those who want to build their own vacuum tubes). paul
Re: LGP-30 Memory Drum Update
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
Re: LGP-30 Memory Drum Update
On 01/04/2017 06:05 AM, Christian Corti wrote: The LGP-30 is similar, but the timing and long tracks (i.e. main memory) are not recirculating. Hence the reason why a word is limited to 31 bits, although the sector holds 32 bits. The last bit must be zero to reset the read circuitry for the next sector. So, there is no inter-word gap to accommodate the write head switching? I guess if everything is hard-synched to the clock track, then you can get away without that. Interesting! Jon
Re: LGP-30 Memory Drum Update
On Wed, 4 Jan 2017, Al Kossow wrote: On 1/4/17 7:03 AM, Klemens Krause wrote: We have a second LGP-30 drum in our museum. It is damaged by water. ... In doing some disk research recently, I came across a footnote for a rather unlikely place to find information on magnetic coatings, which I just got a copy of: Patton "Pigment Handbook Volume II Applications and Markets" 1973 Kurt Kreiselmaier "Pigmentation of Magnetic Tapes" pp 315-329 Nice, the book is available in our library here at the university. I'll get it tomorrow from the magazine. :_ Klemens -- klemens krause Stuttgarter KompetenzZentrum fyr Minimal- & Retrocomputing. http://computermuseum.informatik.uni-stuttgart.de
Re: LGP-30 Memory Drum Update
On 1/4/17 10:19 AM, Al Kossow wrote: On 1/4/17 7:03 AM, Klemens Krause wrote: 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". The was a post application "calendaring" process to get a uniform smooth surface. In doing some disk research recently, I came across a footnote for a rather unlikely place to find information on magnetic coatings, which I just got a copy of: Patton "Pigment Handbook Volume II Applications and Markets" 1973 Kurt Kreiselmaier "Pigmentation of Magnetic Tapes" pp 315-329 Which goes through the whole process at a high level of how magnetic tape is made, including aligning all the magnetic particles on the surface. They also mention sperm oil being used as one of the ingredients (I had wondered if there was documentation for that claim), and about two dozen patents at the end. Sperm oil was a high quality wax/lubricant. Its low viscosity and high resistance to oxidation were its high points. Its likely use was as a plasticize the binder and surface. There is also a lot of information in the book on colorizing agents for plastics. I'll put a scan up today under midwesternUniveristy, where Kreiselmaier was an asst prof.
Re: LGP-30 Memory Drum Update
On 1/4/17 7:03 AM, Klemens Krause wrote: > 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". > In doing some disk research recently, I came across a footnote for a rather unlikely place to find information on magnetic coatings, which I just got a copy of: Patton "Pigment Handbook Volume II Applications and Markets" 1973 Kurt Kreiselmaier "Pigmentation of Magnetic Tapes" pp 315-329 Which goes through the whole process at a high level of how magnetic tape is made, including aligning all the magnetic particles on the surface. They also mention sperm oil being used as one of the ingredients (I had wondered if there was documentation for that claim), and about two dozen patents at the end. There is also a lot of information in the book on colorizing agents for plastics. I'll put a scan up today under midwesternUniveristy, where Kreiselmaier was an asst prof.
Re: LGP-30 Memory Drum Update
On Wed, 4 Jan 2017, Christian Corti wrote: On Tue, 3 Jan 2017, Al Kossow wrote: There are running LGP-30s. Should be short work with a digital oscillosope 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. Klemens -- klemens krause Stuttgarter KompetenzZentrum fyr Minimal- & Retrocomputing. http://computermuseum.informatik.uni-stuttgart.de
Re: LGP-30 Memory Drum Update
On Tue, 3 Jan 2017, Jon Elson wrote: So, does the LGP-30 have permanent storage on the drum, or is it erased by a magnet at every revolution? Yes, the three timing tracks, and the upper half of the instruction counter(!). The upper half containts the number of the following sector and is used to locate the desired sector (either instruction or data). The G-15 modeled the drum just like a mercury delay line, it had a write head, a read head and a bar erase magnet on every line, so there was no gap for the write head to turn on and off between words. The FF that drove the write amp normally recirculated the data from the read head, except when a word was being written. Each drum track had a long line (for program and data) and a short line. Most of the short lines held 4 words, so they were quickly accessible. One short line only held one word, that was the accumulator. The LGP-30 is similar, but the timing and long tracks (i.e. main memory) are not recirculating. Hence the reason why a word is limited to 31 bits, although the sector holds 32 bits. The last bit must be zero to reset the read circuitry for the next sector. Christian
Re: LGP-30 Memory Drum Update
On Tue, 3 Jan 2017, Al Kossow wrote: There are running LGP-30s. Should be short work with a digital oscillosope to capture the flux changes. Hopefully, someone has done this already. Of course, we did this initially in 1999 when we got our first LGP-30, and a couple of times later on. The last time was a few months ago when we suspected a bad sector/track, but it turned out that there was a 50 Hz hum on the read amplifier supply voltage (an electrolytic cap on a module lost its capacity). 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 :-) Christian
Re: LGP-30 Memory Drum Update
On Tue, 3 Jan 2017, Paul Koning wrote: The key questions for reconstructing such a device is what the modulation scheme is, and the pulse pattern. There might be marker pulses for sector start, for example, or that might just be derived from a counter in the controller. It's in the maintenance manual. There is one flux change for a one bit, and a flux change to the opposite direction for a zero bit. All timing is derived from the timing tracks S1..S3. The magic box to reconstruct these timing tracks must be synchronized to the base clock coming from the drum (137 kHz on European machines). The base clock is picked up with a special read head, the clock bits are "engraved" into the drum cylinder, so no need to write this clock track. Christian
Re: LGP-30 Memory Drum Update
On 01/03/2017 01:47 PM, Brian L. Stuart wrote: On Tue, 1/3/17, Cory Heisterkamp wrote: 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. A while back I read a procedure (probably in reference to the G-15). Quite frankly, it scared me a little, but I'll pass it on. The idea is to use sound. The tech would use a screwdriver as a sounding bar between the casing and his ear. Then the head was tightened down until you could just hear it start to brush. I don't remember for sure, but I'd have to think that you would then back off just enough for the brushing sound to stop. I don't recall whether the article said that this was done with the motor running or the drum was being turned by hand, but if it were my machine, I'd set the heads turning the drum slowly by hand and then check for any brushing sound when the motor comes up. YIKES!!! Well, I think the first order of business is to check and possibly replace the drum bearings. Then, get a sensitive dial test indicator (I have an old Federal with .0001" markings, and a Federal electronic indicator that reads down to 50 uInch.) Make up a fixture to mount it on the drum frame and see if the surface of the drum is still true. It is possible that the bearing inner races might need to be turned on the shaft for minimal runout. If the surface has several wobbles per rev, then I think the drum will not be serviceable without turning the oxide true again. I have NO IDEA how thick the oxide might be on these. It did seem like the G-15 oxide was pretty thick, maybe .010" or so. If the above procedure is for real, then it pretty much had to be, to survive such abuse. Doing some totally off the wall calculations in my head, I figured out the data density would have been in the range of 100 bits/inch on the drum circumference. Calculating from the circumference and the number of bits per track, you should be able to calculate the bits/inch. Assuming pretty wide gaps between the head pole pieces, and the bit density, it should not require insanely small head flying height. You can fairly easily get brass shim stock down to .001" or so (kitchen aluminum foil is about .0015") to use for a head height setter. So, does the LGP-30 have permanent storage on the drum, or is it erased by a magnet at every revolution? The G-15 modeled the drum just like a mercury delay line, it had a write head, a read head and a bar erase magnet on every line, so there was no gap for the write head to turn on and off between words. The FF that drove the write amp normally recirculated the data from the read head, except when a word was being written. Each drum track had a long line (for program and data) and a short line. Most of the short lines held 4 words, so they were quickly accessible. One short line only held one word, that was the accumulator. Jon
Re: LGP-30 Memory Drum Update
On 1/3/17 5:42 PM, Al Kossow wrote: > > I think Paul Pierce's machine is at LCM now. They have his LGP-30
Re: LGP-30 Memory Drum Update
On 1/3/17 5:42 PM, Al Kossow wrote: > > Someone should do the same for the surviving G-15s as well. I think Paul > Pierce's machine is at LCM now. > turns out we have it http://www.computerhistory.org/collections/catalog/102728118
Re: LGP-30 Memory Drum Update
On 1/3/17 5:22 PM, Paul Koning wrote: > The key questions for reconstructing such a device is what the modulation > scheme is, and the pulse pattern. There are running LGP-30s. Should be short work with a digital oscillosope to capture the flux changes. Hopefully, someone has done this already. Someone should do the same for the surviving G-15s as well. I think Paul Pierce's machine is at LCM now.
Re: LGP-30 Memory Drum Update
> On Jan 3, 2017, at 6:07 PM, Chuck Guzis wrote: > > On 01/03/2017 01:42 PM, Mark Linimon wrote: > >> Very ambitious. IIRC for the G-15 there is/are (one? two?) timing >> track(s) which were written at the factory. Of course whatever that >> machine was, has not survived. I remember reading that if you lost >> that timing track, your machine was toast. > > > Maybe. ISTR that wehn CE's were working on the CDC STAR station drums, > they routinely rewrote timing tracks. I recall that their only tools > were a scope and a Halliburton CE box. Apparently, the goal was write a > track such that there was no detectable "splice" in the beginning/end of > the track. Pretty much a cut-and-try operation. The fixed head disk I saw rebuilt in the field was a DEC RF11 -- it had basically its entire guts replaced from spare parts. That included a new platter, so its timing track had to be written. The timing track writer box had a knob on it to tweak the clock frequency, and it worked just as you describe: keep hitting the "write track" button and tweak the knob until the track gap checker circuit said the gap size was within the required range. The key questions for reconstructing such a device is what the modulation scheme is, and the pulse pattern. There might be marker pulses for sector start, for example, or that might just be derived from a counter in the controller. paul
Re: LGP-30 Memory Drum Update
On Jan 3, 2017, at 2:22 PM, Klemens Krause wrote: > On Tue, 3 Jan 2017, Cory Heisterkamp wrote: >> >> >> 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 > We relocated some of the heads on our second LGP-30. This is not difficult. > We put 3 or 4 layers of 3 micro-meter kitchen aluminium > between head and drum. If I remember right, the distance is 12 micro- > meter. Maybe, that we made a fine adjustment 3 or 4 layers with the > oscilloscope, to get the same output voltage at the head, than the > other heads. Maybe that 3 layers of 3 micro-meter Al have something > more than 9 micro-meters. > > >> 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. >> > If I counted right on every head bar are 3 unused positions as spare > tracks. >> > >> >> 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? >> > The (german) maintenance manual whose scan is on our website speaks > about 12 micro.meters. > > There are 64 data tracks, 4 timing tracks (including the main clock > at the rightmost position) and 3 tracks for the registers. Most problematic > are the timing tracks. If they are faulty, there is no > simple solution to change the heads, because there is no provision > to write them in the machine. >> > If there are only few tracks defective, and not exchangeable, I > would try to get most of them in the lower adress-room of the > machine, and at least the last track. The first 3 tracks are > used by the "operating-system", program 10.4, and the last track > is used by the initial loader, that loads 10.4 itself. > But timing tracks S1, S2, S3 and the registers themselves must > be functional. > If this is not, a semiconductor drum-emulator ist indeed the > only solution. > If you lift all the head bars 1 or 2 mm, then the drum can > rotate even with this fake. > > Klemens Lots of great ideas guys! After work today I cleaned the 64 track heads and made temporary 0.004 spacers using paper strips and a hole punch. This puts all the head assemblies in the clear for now so nothing can get damaged. Using Klemens suggestion of tinfoil, I made up the perfect 0.001 feeler gauge and set the gaps for the short registers. Adjusting these is a little tricky since you first have to break loose the head securing screw, then adjust the height screw. However, the securing screw can take what is an acceptable gap down to a drum contact once torqued. A little 'back and forth' while stationary and that's resolved but perhaps there's a better way to adjust these while the machine is running (as has been suggested while watching the waveform on a scope). I don't think I'm that brave. Anyhow, my next move is to spin the drum up on the machine (when it arrives) with just the clock and short register heads and then see how much expansion we're looking at. I can then bring in the other tracks heads assembly by assembly once I'm comfortable with the runout and expansion. Spinning it by hand reveals quiet bearings and a nice tight assembly. In the interim I'll start work on the Flexowriter. Something I'm much more comfortable with. -C
Re: LGP-30 Memory Drum Update
On 01/03/2017 01:42 PM, Mark Linimon wrote: > Very ambitious. IIRC for the G-15 there is/are (one? two?) timing > track(s) which were written at the factory. Of course whatever that > machine was, has not survived. I remember reading that if you lost > that timing track, your machine was toast. Maybe. ISTR that wehn CE's were working on the CDC STAR station drums, they routinely rewrote timing tracks. I recall that their only tools were a scope and a Halliburton CE box. Apparently, the goal was write a track such that there was no detectable "splice" in the beginning/end of the track. Pretty much a cut-and-try operation. Perhaps the LGP30 is similar. --Chuck
Re: LGP-30 Memory Drum Update
On 01/03/2017 01:19 PM, Paul Koning wrote: > Metal alloy plating seems common in fixed head disks also, at least > in the ones from DEC I have seen. Making a new drum sounds like a > great class project for an ambitious machine shop student. Modern CNC gear and carbide bits should make this pretty straightforward. One could even fit a new set of modern bearings. --Chuck
Re: LGP-30 Memory Drum Update
On Tue, Jan 03, 2017 at 04:19:01PM -0500, Paul Koning wrote: > Making a new drum sounds like a great class project for an ambitious > machine shop student. Very ambitious. IIRC for the G-15 there is/are (one? two?) timing track(s) which were written at the factory. Of course whatever that machine was, has not survived. I remember reading that if you lost that timing track, your machine was toast. mcl
Re: LGP-30 Memory Drum Update
> On Jan 3, 2017, at 4:15 PM, Chuck Guzis wrote: > > On 01/03/2017 12:57 PM, Cory Heisterkamp wrote: > >> Once I can make sense of the timing tracks, I think I'll proceed with >> this. Not sure how I feel about using a micro-based solution though. >> Just seems wrong : ) -C > > > If enough working heads can be found, the drum probably can be > remanufactured, as according to this: > > http://miriam-english.org/files/drum-computers/drum-computers.html > > the drum was nickel-chromium plated, not ferric oxide. This is what I > would have suspected, as coating equipment and binders would probably be > a far cry from modern technology back then, where precision plating was > already an established art. Metal alloy plating seems common in fixed head disks also, at least in the ones from DEC I have seen. Making a new drum sounds like a great class project for an ambitious machine shop student. paul
Re: LGP-30 Memory Drum Update
On 01/03/2017 12:57 PM, Cory Heisterkamp wrote: > Once I can make sense of the timing tracks, I think I'll proceed with > this. Not sure how I feel about using a micro-based solution though. > Just seems wrong : ) -C If enough working heads can be found, the drum probably can be remanufactured, as according to this: http://miriam-english.org/files/drum-computers/drum-computers.html the drum was nickel-chromium plated, not ferric oxide. This is what I would have suspected, as coating equipment and binders would probably be a far cry from modern technology back then, where precision plating was already an established art. --Chuck
Re: LGP-30 Memory Drum Update
On Tue, Jan 3, 2017 at 1:47 PM, Brian L. Stuart wrote: > On Tue, 1/3/17, Cory Heisterkamp wrote: > > 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. > > A while back I read a procedure (probably in reference to the G-15). > Quite frankly, it scared me a little, but I'll pass it on. The idea is to > use sound. The tech would use a screwdriver as a sounding bar > between the casing and his ear. Then the head was tightened down > until you could just hear it start to brush. I don't remember for sure, > but I'd have to think that you would then back off just enough for > the brushing sound to stop. I don't recall whether the article said > that this was done with the motor running or the drum was being turned > by hand, but if it were my machine, I'd set the heads turning the drum > slowly by hand and then check for any brushing sound when the motor > comes up. > This sounds believable (but scary). With the 64 main heads out of the way, I pulled out a mechanic's stethoscope last night and carefully rocked with the drum back and forth listening to the recirculating register heads. One may need backed off just a little, but the adjustment screws are a little crude. > > Whether or not the drum is restorable, I'd still plan on building a drum > simulator. That way you can get the rest of the machine up and > running without stressing or depending on the drum too much. Plus > if the drum does turn out to be unrestorable, you'll still be able to > run the rest of the machine. As to how to approach the simulator, > I would have to think a C.H.I.P. or a Pi would have plenty of horsepower, > especially if you drop Linux and either run on the bare metal or > as an in-kernel driver in something lighter weight. > > BLS Once I can make sense of the timing tracks, I think I'll proceed with this. Not sure how I feel about using a micro-based solution though. Just seems wrong : ) -C >
Re: LGP-30 Memory Drum Update
On Tue, 3 Jan 2017, Cory Heisterkamp wrote: 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 We relocated some of the heads on our second LGP-30. This is not difficult. We put 3 or 4 layers of 3 micro-meter kitchen aluminium between head and drum. If I remember right, the distance is 12 micro- meter. Maybe, that we made a fine adjustment 3 or 4 layers with the oscilloscope, to get the same output voltage at the head, than the other heads. Maybe that 3 layers of 3 micro-meter Al have something more than 9 micro-meters. 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. If I counted right on every head bar are 3 unused positions as spare tracks. 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? The (german) maintenance manual whose scan is on our website speaks about 12 micro.meters. There are 64 data tracks, 4 timing tracks (including the main clock at the rightmost position) and 3 tracks for the registers. Most problematic are the timing tracks. If they are faulty, there is no simple solution to change the heads, because there is no provision to write them in the machine. If there are only few tracks defective, and not exchangeable, I would try to get most of them in the lower adress-room of the machine, and at least the last track. The first 3 tracks are used by the "operating-system", program 10.4, and the last track is used by the initial loader, that loads 10.4 itself. But timing tracks S1, S2, S3 and the registers themselves must be functional. If this is not, a semiconductor drum-emulator ist indeed the only solution. If you lift all the head bars 1 or 2 mm, then the drum can rotate even with this fake. Klemens Any input is welcome. -C -- klemens krause Stuttgarter KompetenzZentrum fyr Minimal- & Retrocomputing. http://computermuseum.informatik.uni-stuttgart.de
Re: LGP-30 Memory Drum Update
On Tue, 1/3/17, Cory Heisterkamp wrote: > 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. A while back I read a procedure (probably in reference to the G-15). Quite frankly, it scared me a little, but I'll pass it on. The idea is to use sound. The tech would use a screwdriver as a sounding bar between the casing and his ear. Then the head was tightened down until you could just hear it start to brush. I don't remember for sure, but I'd have to think that you would then back off just enough for the brushing sound to stop. I don't recall whether the article said that this was done with the motor running or the drum was being turned by hand, but if it were my machine, I'd set the heads turning the drum slowly by hand and then check for any brushing sound when the motor comes up. Whether or not the drum is restorable, I'd still plan on building a drum simulator. That way you can get the rest of the machine up and running without stressing or depending on the drum too much. Plus if the drum does turn out to be unrestorable, you'll still be able to run the rest of the machine. As to how to approach the simulator, I would have to think a C.H.I.P. or a Pi would have plenty of horsepower, especially if you drop Linux and either run on the bare metal or as an in-kernel driver in something lighter weight. BLS
Re: LGP-30 Memory Drum Update
In a message dated 1/3/2017 11:11:54 A.M. US Mountain Standard Time, el...@pico-systems.com writes: On 01/03/2017 10:58 AM, Cory Heisterkamp wrote: > 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). Most likely the same issue as the G-15 we had. Dust was allowed to get into the drum area and pack under the heads. Probably if you pull the heads and clean them, it will restore clearance. Of course, the bearings may be bad, or will have to be replaced anyway as the grease may have hardened. > > > 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. > If the drum can be set up to run true again (may need attention to bearings) then I think setting the heads up won't be that tough. I suspect it is done with a feeler gauge, this is low-resolution stuff with large gaps in the heads, so the heads probably run with a gap of at least .005" (~ 0.1mm) (I'd think, without actually knowing). > > 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? Well, it could be. That sounds really close for the vintage involved. So, maybe the drum or oxide has swelled. Anyway, if there is much damage to the oxide, it may not make sense to try to repair it. if the heads that jammed it left divots in the drum, or the surface is uneven (likely if swelling actually occurred) then it may require extreme efforts to repair. > > 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. > > > > Why not just replace the whole works? If you are going to replace the long lines with electronic memory, doing the short lines and the clock track should be trivial. I think a mid-sized FPGA could do it all quite easily. My guess is that if the surface is uneven, it may not read back data reliably. The high spots might be fine, the low spots will have dropouts. This is all assuming swelling was the culprit. It is also possible that machined parts suffered stress relief over the years. Wrought metal has stress imparted to it when rolled, and then machining will partially relieve the stresses, causing warpage. The warping continues over time. To eliminate this, critical parts are machined close to size, heat treated to relieve the stress, and then finish ground to exact dimensions. It is possible some of the stress wasn't relieved during manufacture. And, nobody expected a 195x machine to be running in 2017, especially as anybody in the computer business knew those transistors were right around the corner, and would almost certainly replace tubes. Jon Cory - then what holds the oxide to the drum? Horrible thoughts of what happens to binder layers on mag tape... flaking, sticky shed ecccshhh! I deal with this problem all the time on some of the historic video tape we have done conversion on out of our media lab.
Re: LGP-30 Memory Drum Update
On 01/03/2017 10:58 AM, Cory Heisterkamp wrote: 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). Most likely the same issue as the G-15 we had. Dust was allowed to get into the drum area and pack under the heads. Probably if you pull the heads and clean them, it will restore clearance. Of course, the bearings may be bad, or will have to be replaced anyway as the grease may have hardened. 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. If the drum can be set up to run true again (may need attention to bearings) then I think setting the heads up won't be that tough. I suspect it is done with a feeler gauge, this is low-resolution stuff with large gaps in the heads, so the heads probably run with a gap of at least .005" (~ 0.1mm) (I'd think, without actually knowing). 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? Well, it could be. That sounds really close for the vintage involved. So, maybe the drum or oxide has swelled. Anyway, if there is much damage to the oxide, it may not make sense to try to repair it. if the heads that jammed it left divots in the drum, or the surface is uneven (likely if swelling actually occurred) then it may require extreme efforts to repair. 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. Why not just replace the whole works? If you are going to replace the long lines with electronic memory, doing the short lines and the clock track should be trivial. I think a mid-sized FPGA could do it all quite easily. My guess is that if the surface is uneven, it may not read back data reliably. The high spots might be fine, the low spots will have dropouts. This is all assuming swelling was the culprit. It is also possible that machined parts suffered stress relief over the years. Wrought metal has stress imparted to it when rolled, and then machining will partially relieve the stresses, causing warpage. The warping continues over time. To eliminate this, critical parts are machined close to size, heat treated to relieve the stress, and then finish ground to exact dimensions. It is possible some of the stress wasn't relieved during manufacture. And, nobody expected a 195x machine to be running in 2017, especially as anybody in the computer business knew those transistors were right around the corner, and would almost certainly replace tubes. Jon
