Provenance Details of some Original Kenbak-1's.

John Blankenbaker's Three Machines:

When Kenbak Corporation closed down business in 1973, John sent a huge load of unsold and partial machines, parts, and documents to "CTI Educational Products" in South Carolina, who had plans of manufacturing and selling it under their own brand.  But he retained 3 machines for himself: the first prototype, one working production model, and one non-working production model.   

John donated the working production model to the Computer Museum in Boston in 1986, when they named the Kenbak-1 the first personal computer. That institution struggled in the late 1990's and finally closed doors and shipped most artifacts to the Computer History Museum in California around 2000,  This was before they had a physical museum building ready, so much of the collection was stored in an old building in Moffet Field, California, called the "Digibarn."  A picture of the Kenbak-1 in the Digibarn documents it there in 2001.  Somehow the extruded aluminum handles were lost sometime between 1986 (when the machine was pictured with the handles) and 2001.  The Mountain View museum was completed in June 2003, and the Kenbak has been on public display since.

John's non-working production model (serial #183) was assembled in 1971 or 72, but never worked right.  John finally fixed it around 2010, replacing several IC's and at least one transistor.  It was missing one aluminum handle on the side, and John had to get a new one fabricated.  When he got it working, his daughter sold it on eBay in 5/2010 for $25,600 to a collector in Monza, Italy , who then re-sold it on eBay February 2016.  It is now in an amazing private collection of computers in Massachusetts, and viewable on his website at

John finally decided to sell his first prototype machine via Bonham's Auctioneers in 2015.  He found that it stopped working (after 40+ years) and John had to replace a shift-register to get it working.  It sold for $31,250 to a retailer of scientific and technical instruments (Jeremy Norman and Company, Novato, CA) who listed it for sale in their "Catalogue 54" for $65,000Achim Baqué of Germany eventually bought it from him for an $41,250.  Achim maintains several excellent internet pages about his acquisition of the Kenbak-1 prototype.

John Blankenbaker, showing his 

prototype machine (YouTube, 2010)

The working production model, in Digibarn, in 2001, missing the handles which were present when donated.

The Nielsen "Hoard" of Eight:

Robert R. Nielsen Sr. of Charleston, South Carolina described himself as a "Pioneer of Computing and Kenbak-1 Expert" among other credentials such as "Treasure Hunter."  He learned data processing in the US Navy, then opened up schools to train GI's in computers and electronics.  This eventually became the "Nielsen Electronics Institute."  He was approached by "CTI Educational Products" in late 1973 when they were considering buying out the Kenbak Corporation and wanted Nielsen's opinion on the computers.  Nielsen loved the machine, and purchased several to teach computer programming in his school.  CTI had plans of reproducing the machine, but their sales force was unable to sell many (any?) so they never started production.  Robert says he's certain they never made a single machine out of scratch, and doesn't think they sold any, other than to him.  When CTI went out of business soon after, Nielsen purchased all of their Kenbak-1 related items at auction, and even told me he purchased the "intellectual rights" to the Kenbak-1 computer.  The eight computers remained in use in his school into the mid 90's.  He explains how very early on they noticed the machines would fail due to overheating, but they found that drilling holes in the top solved that.  He also explains how  the buttons could break off the front panel if pressed too hard, so he would frequently have to replace them.  When they ran out of the original pushbuttons, the school tried replacing them with blue momentary toggle switches (seen on Nielsen 6) but Nielsen never liked it.  When Nielsen's school finally closed in the late 1990's, he put his eight computers in a big box in his garage, which he said he kept during several home moves, and they weren't packed well, so broke several switches.  But he did keep and preserve them.

All of the eight computers in Nielsen's school had holes drilled in the top of the case, which helps distinguish them.  And some, if not all, of the computers sold by CTI either had the Kenbak-1 logo covered up with a foil sticker saying "CTI" or had replacement front panels with a "CTI" logo silkscreened on, but no slot.  While those foil CTI stickers appear in some early photos, now all of them seem to have been removed, revealing the original Kenbak-1 name.  

In the early 2000's Nielsen began to email computer museums to see if anyone would buy his Kenbak-1 computers.  None had any interest in paying, but would accept them as a donation.  Eventually he emailed Herbert Eisengruber of the "Nova Scotia Computer Museum" in Canada.  Herbert had a small museum, focusing on computers, video games, and robotics, in Annapolis Royal, Nova Scotia.  He was quite interested in the Kenbak-1, but didn't have a lot of funds.  Herbert offered Nielsen a used laptop computer in trade, and soon after mailing off the laptop, he received his first Kenbak-1 (Nielsen #1) in April 2003.  A few months later, Nielsen contacted Eisengruber again, offering to sell six more computers and a large lot of documentation for $15,000.  This was a lot of money, but Herbert got a loan from his parents, and drove down to South Carolina to get the machines in September 2003.  Robert Nielsen then held onto his last computer until  May 2011, when he listed it on eBay.  It didn't initially sell due to a high reserve, but he eventually sold it to (to Lonnie Mimms, founder of the Computer Museum of America for $20,000, along with a lot of memorabilia regarding his technical school and the Kenbak-1.   Robert Nielsen died July 28, 2020.

Herbert Eisengruber then owned 7 Kenbak-1 computers which were on public display in his Nova Scotia Computer Museum.  He advanced knowledge of the computer by making an early list of all known existing machines, and was the first to distribute some of the original schematics and state diagrams.  He also presented his research at a display at the Vintage Computer Festival.  

But eventually his  Nova Scotia Computer Museum closed down and Herbert moved to Calgary.   He sold most of the Kenbak-1 computers for around $10,000 each.  One went to a collector in Middleton Nova Scotia (Nielsen #1) but was then sold on eBay in April 2019.   This machine was then acquired in late 2022 from the Computer Museum of America.  One went to Vinal Applebee of the "Maine Computer Museum" which never opened (Nielsen's #4, Serial #185) who sold it to a UK museum.  One sold to a collector in Minnesota (Nielsen's #3) and one one sold to Lonnie Mimms, founder of "Computer Museum of America" in Roswell, Georgia (Nielsen's #2, the one with odd blue toggle buttons.)  Herbert sold at least two on eBay.

Today, six of the seven Eisengruber Kenbak-1's are accounted for with new owners, but one (Nielsen5) remains in in an unknown private collection, without any sightings for almost 15 years.  

The 7 Kenbak-1's from the Nova Scotia Computer Museum/Herbert Eisengruber (Nielsen1-7))

Robert Nielsen with his 

eighth and last (Nielsen8)

from a YouTube video.

Nielsen with six of his computers, September 2003 (photo courtesy of Herbert Eisengruber)

Tom Crosley's Kenbak-1:

Thomas (Tom) Crosley is the only private individual we know of who purchased a new computer right from the Scientific American advertisement.  His computer became the first computer well documented on the internet, inspiring many to study and make their own.  He purchased his Kenbak-1 in 1971 or 1972 after seeing the advertisement in Scientific American.  He graduated Iowa State University in electrical engineering, then went back for a master's degree in computer science in 1970.  He wanted a computer of his own to help him practice machine code programming.   He told me "It was a major purchase -- $750 in 1971 is something like $5500 today.  I was only making about $11,000 a year."  He liked the machine, and used it throughout his college years even though he had access to a lot of other computers.  He told me "The Kenbak actually had a more useful instruction set than the PDP-8."  In 1975 he bought a Sphere-1 computer, and commented "It had a 6800 processor, which I was attracted to because the register set almost exactly matched the one in the Kenbak -- two accumulators A and B, and an index register X.  It came out about the same time as the Altair 8800, but I never liked the Intel 8080 instruction set."

Crosley combined his electrical and computer skills by building an ASR-33 teletype interface for his Kenbak-1.  This solved the 17 year long mystery of why Erik Klein's computer had some an extra integrated circuit soldered into the usually empty IC99 spot, and had extra wires added.  Tom says he could load in a short bootstrap loader, and then could automatically load in programs via the ASR-33's keyboard or paper tape.   He wrote letters published in the Amateur Computer Society newsletter telling how he had expanded the memory, and was working on other interfaces, and hoping to make contact with other Kenbak-1 owners.

The ASR-33 teletypes were very common computer keyboard/display terminals, until video terminals became available around 1975 and 1976.

In late 2003 he was moving from California to Arizona, and posted a message to Erik Klein's Vintage Computer Forum asking for advice on it:

Dec 31, 2003:

We are moving shortly, and while cleaning out our garage I came across my Kenbak-1.

I understand this computer won The Computer Museum’s “Earliest PC Contest” back in 1986.

I figured it is rather rare, since only some 60 or so were ever built, but doing a quick search on the web I discovered there may only be ten others still in existence.

It appears to power up okay. Here's a photo I just took:

(photo removed)

Some of the front panel switches are loose, apparently there were glued onto the back of the panel but that is easily fixed. But they all work -- the lights change when I push the buttons. Unfortunately I no longer have the manual for it (at least it hasn't shown up yet.)

Earlier this year, I donated my other vintage computer (a Sphere 6800) to a museum in California. It wasn't running however. I don't think I want to just give my Kenbak away, given its scarcity and since it seems to run.

Is it possible to donate a computer like this but retain title to it (e.g. loan it to a museum?)

What would you do with it? I can't take it with me to our new house so I have to decide something soon.

Thanks for any input.


It was suggested to sell it on eBay, which he did, and Erik himself was the winning bidder at $2000.  This was a very reasonable price at the time.  Erik posted detailed pictures and information on his "Vintage-Computer" website, and countless people learned about this previously little known computer.  Tom is now retired, but shares his experiences and insight frequently online on Quora, which is how he was tracked down.

There's probably hasn't been a more documented machine than this.  Erik put great high resolution photos of every part of the computer to his vintage computer website, and that did more to spread knowledge and enthusiasm for the Kenbak-1 than anything, other than the designation of "first pc" by the Boston Computer Museum 20 years earlier.