Archive for September, 2013

18th September
written by Todd Harrison

A good friend gave me this 1971 vintage Monroe 1651 engineering calculator.
Please watch (part 1) if you want to see the full introduction & teardown.

Fair warning: This is a half hour video of me powering on and simply putting the calculator through some calculation exercise to demonstrate its capabilities. It will be dry watching unless you’re a calculator freak like me or you enjoy watching some old nixie tub calculator porn.

<video – power & functionality>

What makes this old calculator so interesting is how much electronic computer power it had in the day. It was feature rich, agile and even small comparatively for the early 1970’s. The nixie tube display also adds a warm glow of appeal not commonly found in too many surviving electronics of yester year. Let’s don’t forget to list rare! This example of old tech is museum quality in functionality as well as scarcity. Unfortunately for this example any functionality requiring the “second function” feature is not currently working. I have my eyes and ears on the lookout for spare parts and service manuals but nothing yet. If you know of any resources please contact me, my email is in my “about me” page on (a bit coded to avoid some web bots but you humans will figure it out).

I did get in contact with the original owner of this calculator who bought it for his work with aviation calculations in 1971. At the time of this write-up he is 77 years old and I’m trying to coordinate an interview with him. I have a long list of questions so if that manifests I will update this page or post a new article on this calculator.


Comments Off on Monroe 1651 Nixie Tube Engineering Calculator From 1971 Part 2 – Power on & Functionality
3rd September
written by Todd Harrison

I received this very nice gift from an old friend about a year ago. It is a Monroe 1651 engineering calculator from 1971. Sometimes called a scientific calculator, sales were targeted to engineers as well as mathematicians. It is in magnificent condition considering its age and even came with the original dust cover. Only the power cord had degraded with age but that was easy repaired. I have waited a long time to power it up but wanted to have a variac to bring it up slowly to 120v AC the first time. I didn’t want to risk flipping it on a full 120v AC and having one little problem fry irreplaceable components. In this video I only give an introduction to the 1651 and a full teardown. The power up and and functionality tests is now available in (part 2).

<Video intro & teardown>

Here are some helpful links to information I sourced during my research.
This 1665 is a very close functional calculator to my 1651 and was a wealth of information.
List of Monroe calculators from this time range and some old ads.
This is a listing to another 1651 calculator like my 1651.
Here is a listing for a 1655 which is just like my 1651 but is programmable and uses a punch card reader! COOL!
I found this video of a much abused 1655 in the wild uploaded on YouTube at channel “qwaqwa1960”:


Photo Gallery

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Comments Off on Monroe 1651 Nixie Tube Engineering Calculator from 1971 Part 1 – Intro & Teardown
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