LINC tape drive

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DEC equipment I have

To see some DEC equipment I have, check this Web page.

LINCtape and LINC

[LINCtape drive]A few years ago, I picked up this DECtape-like drive. In Aug 2009 I realized it's a LINCtape drive, probably produced in 1966 for a LINC computer of the period. Here's the bottom view. The LINC was an early digital computer design of the mid to late 1960's, produced to establish the utility of on-site computing for biomedical research. It influenced DEC, who produced a LINC/8 computer. Work was done at Washington University and at MIT. Check other Web sites for the history of the LINC computer.

I found on the Web, some restoration work done in 2007-08 to restore a LINC system now at Digibarn in northern California. Check the Digibarn site for details of the restoration work and their discussion about the LINC. Bruce Damer of Digibarn got me in touch with the LINC developers in 2009, and in 2011 Jack Rubin obtained LINC documents from Digibarn and provided images of them to me. - Herb

Where did my drive come from?

Here's an image of the top of the LINC tape drive now at Digibarn. Compare to the top view of my drive and I think you will agree they are near identical.

A lable on the bottom of the drive says "US Govt Atomic Energy Commission, Manomet Bird Observatory, Contract #AT(11-1)2308, item #17". From some Web research, I found that physicist Constantine J. Maletskos, Ph.D. worked with the Manomet Bird Observatory in Massachusetts (USA) from 1975, and served on their board until 1995. Funding from the AEC supported monitoring of birds to detect potential radiation contamination from a local nuclear power station, Pilgrim Station. The Avian Nuclide Project, a first for wild bird radioecology, was directed by Kenneth A. Youngstrom in 1975.

"Avian radioecology on a nuclear power station site. Final report". Levy, C.K. ; Maletskos, C.J. ; Youngstrom, K.A.
1975 Jan 01, Dep. NTIS, PC A06/MF A01; OSTI ID: 6623045. DOE Contract Number EY-76-S-02-2308.
Check the OSTI Web site to reference the document.

The Manomet Center Web site is at this Web link.

A "Oral Histories, Human Radiation Experiements" WEb site has: discussions with Dr. Maletskos about his work with Manomet.

my LINCtape drive

[LINCtape drive bottom]In this bottom view of the drive two of the square AC capacitors are missing. Note the date code on the capacitor, 24th week of 1966. The back of the drive shows the connectors to the drive, the AC outlet and AC fuse. Like the later DECtape TU55 and TU56 drive, this drive has a ten-track tape head and guides for 3/4-inch magnetic tape. Here's a top view of the drive.

This side view shows some of the electronics, the AC motor, and the belt from motor to tape reel. Each reel has a motor, driving the reel via a belt and speed-reducing pulley. (Note the poor condition of the rubber and cloth belt.) The nameplate on one motor identifies it as an AC motor, consistent with the AC cap used with each motor. This side view shows more of the electronics. Note the old-style selenium rectifier, the square-ribbed device behind the motor: four of them are visible in the bottom view of the whole drive. Components are on a phenolic board at the back of the drive, mounted on posts, hand-wired and cabled.

In Jan 2015, due to some interest in my LINCtape drive, I reviewed and gathered LINC document specific to my drive. Here's a set of drawings and schematics for my LINCtape drive. they are exerpts from the DEC LINC-8 Maintenance Manual, Vol 2, Nov 1967. This is described on as "F-L87_LINC-8MaintVol2_Nov67.pdf". I find it informative, that the drawings of the physical drive I have, match my drive. If my exerpts don't include critical drawings from the Maintenance Manual, let me know. I've "covered" the drive and some of the immediate modules and cabling from the LINC-8.

Restoration of my LINCtape drive

In the second half of 2009, I was in touch with some of the LINC developers who are still at work, restoring a few LINC systems or cooperating with the "Digibarn" and their LINC system. I hoped to obtain some engineering drawings of the LINC, which at that time are on two hundred 24 X 36 inch sheets and so difficult to copy. But I've had discussions about the LINC and about my drive, and how to make copies of these drawings.

Most of the logic and electronics for use of the drive, as Maury Pepper told me, "is in the LINC frame -- a six foot tall, double sided 22" rack/cabinet. The drive by itself has no logic.". The missing relays are, I'm told, Allied Controls model TDX 1349. So, any testing or operation of my drive will require some kind of controller, plus most likely some read/write analog electronics, plus power of course. I'm working to get some documents, to see what I have and to assess what I need to do. I've been told the other LINC drives required replacement of bearings and of course belts.

By 2011, a set of original LINC documents have been digitized and are available. See the Web links section below for details..

AC capacitors

Two of the square AC capacitors are missing. They are Aerovox brand, Sprague capacitors, 18970-6, 2FD 330V AC. They measure 2-1/4" X 1-3/4" X 1". Each is a 2uFd 33V AC capacitor for an AC drive motor. Note the date code on the capacitor, 24th week of 1966. Apparently, this may be a "motor run" capacitor, because it has smaller capacity than a "motor start" capacitor. But I don't know.

Tape head

[LINCtape heat] [LINCtape heat]

In Aug 2020, I was asked to detail the tape head. The photos shows the ten-track head and some labeling. Here's a closeup of the label on the head. It says, "gjm MAGNETICS DIV / SER NO 2769 / 1733 FLOWER ST / GLENDALE CALIF". The other head has a similar label and slightly different serial number. Some Web searching finds a company, "Western Magnetics, a division of GJM Inc." at that address; as part of a list of small EDP peripheral equipment shops. The list is from Congressional testimony in a 1967 document on government procurements.

Tedious Web searching eventually found that "Western Magnetics Inc" a Calif. corporation at that address, was established in Dec 1 1981 and operated for 9 years and one month; CEO William P Dingsdale. And: Western Magnetics Inc, date established Apr 15 1968, operating for 19 years and 7 months, (merged out). Datamation for June 1969 mentions on page 258 that "William P Dingdale has been elected President of Western Magnetics Inc ... producer of magnetic tape heads".

LINCtape relays

One of the first things I'll need are relays; my drive has all of them removed. As noted above they are Allied Controls model TDX 1349. Here's the socket for one of the relays.

In late October 2009, thanks to David Gesswin, I was directed to "bitsavers" to obtain some LINC-8 documents. One of those documents includes a description of the LINC tape drive, or something very similar; the other has the engineering drawings for it. This gives me the information I need on the LINC relays. These documents help to describe the relay, as best I make sense of them. And I'll need all that info, because it's pretty likely these are not available anymore.

Some searching of Allied Controls references and current catalogs, via the Web, provided no references to "TDX" model relays. The LINC docs suggest these were custom-built by Allied for LINC. In Oct 2010, thanks to Jack Rubin providing clearer LINC documents, the relay and socket were identified as follows. The 6 relays are called out as "Allied TDX 1349" mounted in "Allied 30055-20" sockets. These relays are unique even for the time, because of the internal transistor driven by -3 volt logic (I think) to switch the coil. The voltage supply to the relays is -15V (relative to solenoid return).

However, A photo of these relays from the Computer History Museum shows additional components inside the relay, not shown schematically on the LINC. I see a 1.3K ohm resistor for example.

Details of the TDX-1349

[LINCtape TDX 1349]

[LINCtape TDX 1349]

Here's a snip from one LINC document showing a relay schematically. After I got the LINC document collection from Jack Rubin in July 2011, I found LINC document 1349 had more specifications and photos. Here's a photo from the LINC documents of the relay assembly.... ...and a photo of the relay schematic. Here's text of information I derived from all LINC documents.

[LINCtape TDX 1349]

[LINCtape TDX 1349]

Aug 2011:Thanks to a Web search by David Gesswein, and the kindness of University of Iowa professor and PDP-8 collector Doug Jones, I've acquired an in-the-box TDX-1349 relay in Aug 2011. Dr. Jones sent the relay, photographed here to left and right. I have little doubt, these were custom-made devices. This particular relay, though still in its original box and packing, shows signs of use with solder on some pins.

alternative relays

I could add a PNP transistor, etc to a 12V to 15V DPDT relay of the same size, voltage/current and socket compatibility, with 1A 124VAC contacts at pins 14-15-16 and 5-6-7. 16 and 6 as common for each set. If I remember how relays are represented on a schematic, the normally closed (unpowered) connection is 5-6 and and 14-15. Coil is pins 1 and 4, the PNP is emitter to 2, base to 3, collector to 4. So an adapted relay would have to have pins 2 and 3 available; most relay models don't have those pins available.

By July 2011, I had acquired some 5-volt relays, unused and in good quantity. My thought is to make an adapter of PC boards, capable of plugging into the LINCtape relay socket while holding one of these. There may be issues of switching speed and contact current capacity.

the Zettler brand AZ 2732-125-2 relay is marked "8 AMP @ 24VDC or 115VAC" and "1/8 HP 120 VAC MTR LOAD". It's DPDT like the LINC relay. The physical form is very different, and this is a sealed relay. Documentation for it specifies a "must operate" voltage of 3.5V, normal voltage 5v, across 38 ohms. (My ohmmeter reads 40 ohms.) Specs say it should operate with about 337 mW of power, suggesting an operating current of 67mA or so.

the POTTER & BRUMFIELD (AMF) brand RK 11Z 4.5 relay is marked "5A 277VAC; 1/4HP, 250VAC; 240VA 240VAC; (coil) 4.5V; 5A .2A INd. 250V AC; Lgr. C250" Documentation also says "must operate" at 3.5V, working voltage 4.5V, maximum 7 volts. This relay can be opened, useful if I need to adjust it. Measured coil resistance is 43 ohms. Specs say it should operate with about 261 mW of power, suggesting an operating current of 50mA or so.

The seller of these two relays advises: "If you have to tweak contacts, then the Potter & Brumfield relays are by far the right choice. They open easily. The Zettlers are ultrasonically welded shut. They can be cut carefully, and glued back if desired, but it is WAY more effort than the P&Bs. Two jeweler's drivers on either side at the retaining rectangular posts, and you're in. And they just snap back together. " He suggests I may be able to wire two relay sockets together to achieve an adapter.

In June 2011, I got a photo look at the relay on David Gesswein's LINCtape drive. Looks like 12V not 3V, the print is "R10-E2-Z2-S800 12VDC 7232-2" and no sign of a transistor/resistor inside the relay. This drive of David's is different from mine.

LINCtape belts, more docs, other tapedrives

Prompted a request by David Gesswein in June 2011, I measured the dimensions of a LINCtape belt I cut off. The belt is 8-1/4" long, 1/4" wide, and has 12 teeth per inch. The belt is made of a kind of cloth with several threads along its length, presumably to resist stretching. The teeth are probably of a molded plastic, deteroriated in these 40-year old belts. With the belt removed, you can see the material embedded in the cogged teeth of the two gears, the motor and the tape hub. The motor shaft is open at one end, the hub shaft ends in a bearing in a plate which would need to be removed to change belts.

[Gesswein LINC tape drive] David contacted me because he obtained a Computer Operations Inc CO-600 LINC tape drive, part of a PDP 8/L. David's drive is similar but not identical to mine; he wanted to know if I had found belts for my drive. Here's some photos of his drive's motor sections, to see belts and drive mechanics. heads up view, the heads down view.(note the drive motors nameplate, then follow this link) I contacted Jack Rubin for more information, because he was in process to copy the LINC documentation held by Digibarn. See the Web links below to obtain the scanned documentation.

David and I discussed belts during June and July. I cleaned one of my drive's belts off and test-fit some belts from a sewing machine store. With Jack's docs, David found the LINC specs for the belts (very similar to my findings) and pointed me to a source. Here's a Web page with details of my successful work on my LINCtape drive belts. In July I sent duplicates of my LINC belts to David. Unfortunately, they were too short in length. David sent them back in Sept with some DECtapes and empty reels. (I'll add a link to David's drive page when he works on his LINC/8, otherwise check

DECtapes, LINCtapes, Astrotapes

Doug Jones provided another point of DECtape - LINCtape reference, when we discussed his PDP-8/L system with its tape drives similar to mine. He has an Astrotype (rebadged PDP-8/L) system acquired some years ago, follow the link for details.

In Aug 2011, I recieved some "DECtapes" from Doug Jones. Doug suggested a problem of "fit", of tapes to hubs on his drives. Then in Sept 2011, I received some LINCtape and DECtape tapes and reels from David Gesswein. For details and physical dimensions, see this linked Web page about tapes and hubs as measured by me.

LINKtape or DECtape motors

[LINCtape drive motors?]

In Aug 2011 I won an eBay auction for "(3) Elinco AC Torque Motor 40V 40Hz". These caught my eye originally, because I was searching ebay for any kind of LINC part or reference. The LINC uses 40Hz motors, I believe that was my search term. In this case, the seller had no idea what these motors were for, they were among many other used parts they sold. In any event, the photo of them, including the tape-mount head, looked like motors (servos) I've seen on LINC drives and on DECtape drives. The nameplate description seems to be similar to LINC motors. They need 100 uFd 70V capacitors to operate them.

Later I discovered these were used on one model of DECtape drives; I sold a pair to a drive owner who had damaged motors, in 2014. I retained the hubs. - Herb

In June 2019 I acquired an Elinco DPJJ-3197 torque motor that has compatible specs, to the motors on my LINCtape drive. Here's an image of the motor.

More Web links, LINC documents

LINC history

The National Institutes of Health, "Laboratory Instrument Computer (LINC)- The Genesis of a Technological Revolution"
Charles Molnar Web page at Washington University
Wash Univ. Biomedical Computer Lab and LINC Look at the annual progress reports, a LINC was in use through 1980.
Charles Babbage Institute, interview of Severo Ornstein in 1990

Digibarn, Jack Rubin and LINC documents

I found on the Web, some restoration work done in 2007-08 to restore a LINC system as done by some of the early developers of the LINC. They worked on it at Washington University, then transported the system to Digibarn in northern California. Check the Digibarn site for details of the restoration work and their discussion about the LINC. In 2009 Bruce Damer of DigiBarn introduced me to those developers. I corresponded with the about the drive I have, and encouraged them to obtain scans or photocopies of their documents. In due course, Jack Rubin obtained the LINC documentation from DigiBarn, made images of them during 2010-2011. In July 2011, Jac provided the imaged documents to me, among others.

As of July 2011, Jack was distributing DVD's of these documents and intended to provide them to an online archive - I'll add a link here when that occurs. I can postal mail a CD-ROM copy (over 300MB of PDF documents) upon request for $5 including postage, within the USA. Contact me or Jack Rubin to obtain a copy.

Washington University today and LINC

Washington University had a LINC computer on display in November 2010 at their Bernard Becker Medical Library. This is a "display" restoration by the LINC restorers at Wash U., not a working system. As of summer 2011 it is just inside the main entry of Brauer Hall, which houses facilities of the Dept. of Biomedical Engineering. The exhibit may travel elsewhere over time. A brochure was created about the display and LINC history, this links to that PDF.

I got an update from Maury Pepper in Nov 2013 about the Wash U LINC "team" as follows: "There was a reunion at Washington Univ. last May, for the two computer labs BCL and CSL that existed side-by-side from about 1964 to 1990. We got the display LINC running, but could not get either tape drive to function reliably -- not even enough to load the operating system." "[J. Walter Woodbury,] one of the original researchers who assembled and then evaluated a LINC back in 1963-65, came to the reunion with his son. The two of them have kept that LINC running."

The Web link for the reunion, is to a Web site supporing that event. The Woodbury Lab is at Brigham Young University; the Web link is a brief description of the status of the original LINC computer. - Herb Johnson

David Director, a student with LINC access

I corresponded in July 2011 with David Director, who shared his LINC experiences with me as follows.

"I'll be interested to see how you do on the LINCtape.  I used to have a 
couple of actual tapes sitting in a box somewhere, and they may still be 
around.  The University of Pennsylvania had a LINC when I was in school, 
in the same Biology building where I worked.  As all of the student 
techs used to hang out together during the nights when we were keeping 
tabs on the professors' experiments, we often hung out down there and 
played with the LINC, displaying Snoopy on his doghouse and other fun 
and games.  We had a double-wide console that you could sit at, with the 
rack nearby.  And it was the expanded model, with 4K of 12-bit memory.
.....I worked in the building starting in fall of
1964, sophomore year, for a professor who was investigating the response of
embryonic plant cells to various environmental conditions to determine what
caused them to differentiate into root and stalk.  I was into electronics at
the time, with a ham license (K3PMR) and a first-class commercial license
(engineering at WXPN, which at that time was entirely student-run).  I built
him an electronic data recording system to capture our data on paper tape,
but also spent a lot of time in the middle of the night overseeing
experiments and trying not to freeze; most of the work was done in a room
around 50 degrees.  In between I'd go down to the basement, where they were
using the LINC for some kind of neurological research on rats.  I learned
some of my first programming skills there, along with the larger CDC-160
department computer with its 32K of memory and printer, card reader, and
paper tape.

I did have some brief later contact with both the LINC-8 and the PDP-12, as
well as working with the regular PDP-8, the PDP-6, PDP-15, and PDP-11/34.
Actually, the 11/34 was the start of my video store software; I'd been
developing a fancy dual-screen analyst workstation based on that machine,
and many of the features of that went into my user interface."

- David Director

related LINC, PDP-8 sites & correspondence

The "bitsavers" archive has some LINC documentation. is one link to that collection. Another link is on this part of their site. They may have additional information at other places on their site. The home page has links to mirrors of the bitsavers collection as they recommend.

Courtesy of my friend and colleague David Gesswein, here's details on repairing his DEC TU56 DECtape drive. For his work on a TU10 drive, involving motor and tape path repairs probably like what I'll have to do, here's his pages on a TU10 restoration. See this linked Web page about some of David's LINCtapes and DECtapes as physically measured by me.

University of Iowa professor and PDP-8 collector Doug Jones describes a number of PDP-8/L's on his Web pages. He's assisted me on parts and on mechanical features of the drives. He provided several DECtapes used on an Astrotype editing system, and a LINC relay somehow available at the University: my thanks to him. I describe the relay in notes above. The tapes, and the Astrotype system Doug got them from, are described in this Web document. See this linked Web page about Astrotype tapes as physically measured by me.

I corresponded in July 2011 with David Director, who shared his LINC experiences with me. See the notes above.

In 2015, I've had some correspondence with Charles Lasner, which encouaged me to gather more documentation on my LINCtape drive. I've updated this Web page accordingly.

A Wash U alumnus and his LINC experiences

Government procurement of Data Processing Equipment in 1967

"Economy in Government Procurement and Property Management": Hearings Before the United States Joint Economic Committee, Subcommittee on Economy in Government, Ninetieth Congress, First Session, on Nov. 27-30, Dec. 8, 1967. Appendix 6 listes "independent Computer Peripherial Equipment Manufacturers and Glossary of Terms". Pages 531 and following list several "Independent Computer Peripheral Equipment Manufacturers and Glossary of Terms". It may be part of Congressional testimony by Lewis R Caveney, asst to the VP, Bryant COmputer Products, division of Ex-Cell-O Corp, Walled Lake MI. He claimed to be "an unofficial voice for the independent manufacturers of computer peripherals" who "nearly all suffer from the problems I wish to bring to this committee's attention". (p281 following)

Said problem, is the freeze-out of small independents from selling directly to the government purchases of large EDP systems. (Electronic Data Processing). For instance, buying one memory system from an independent instead of five from the OEM could result in substantial savings due to less total size and less maintenance and floor space costs. This may be testimony related to regulating large computer companies to provide standard interfaces, so competative devices could be purchased and connected to large systems with full or superior compatibility. .Mr. Caveney provided the list of companies (p293-4) which was published as Appendix 6.

A discussion ensues with Senator Proximire, about the expertize needed to purchase and assemble these peripheral units - can the Armed Forces afford such people, or can only large EDP companies pay such people what they are worth? Such expertize is not necessary: "This is because the end uper today - banks, industry, small busineses - have become more knowledgable of computer systems, and they are saying now to the computer manufacturer 'Look, we do not like some of your peripherals, we want Joe's over here, who makes a peripheral that meets our requirements better and it is cheaper.' They will say 'You can't have that, we don't sell that.' They say 'Well, I will get this marriage counselor, he will interface it.' And this is what the market trend is right now." (p 296) Several senators discuss the issues and merits of procurement from many small companies versus the complexity of keeping track of them. Thus the reference to "marriage counselors" versus "wedding counselors". - Herb Johnson, Aug 2020

Herb Johnson
New Jersey, USA
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