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Donner 3500 - an early portable computer
  by Bill Degnan - 05/25/2009 17:58
The 1959 Donner 3500 portable analog computer. Click for larger image.

Pushing the exploration of portable computing one giant step farther (for me), here is a quick glimpse of the Donner 3500...My copy of the instruction manual was published in 1960, after Systron merged with Donner to form Systron-Donner Corporation. The manual depicts a Model 3500 with leather handles on the sides. The computer I have has metal handles on top, and I am unsure if this means it's an earlier model made before the merger or if the handles were added by the owner. Because they are symmetrical, I'd like to believe that they are factory/original handles. Also, this computer's serial number is 107, which also indicates an earlier version. Serial numbers can be deceiving however.

The computer id plate on the back of my 3500 says "Donner Scientific Company".

I do not have the "3571 Potentiometer Strip" option installed to the top back of the 3500, indicating that this computer may have been used with an external control device or oscilloscope.


NEXT: Post a PDF of the instruction manual.

Donner 3500 Schematic
  by Bill Degnan - 05/29/2009 10:37
Donner 3500 Schematic

Donner 3500 Tube Layout
  by Bill Degnan - 06/18/2009 22:52
There are 6 control boards in the Donner 3500, each has a set of tubes. This weekend I tested every one of the tubes, they all work. I used a Heathkit tube tester.

Voltage Regulator card for the Donner 3500 analog computer. This card is inserted into the left most slot on the blue ribbon receptical bus back plane.

Viewing from the back of the unit with the door open:

1) left-most card is a voltage regulator, tubes from left to right:

2) The remaining 5 cards are the same, the tubes from left to right are:

ECC 83 / 12AX7
ECC 83 / 12AX7
- NOT A TUBE (It's a relay)
ECC 83 / 12AX7

3) There are two tubes attached to the chassis to the right of the 6th card. The tubes in this space are both marked OB2

Donner 3500 As Direct Voltage Meter
  by Bill Degnan - 07/17/2014 21:38
Donner 3500 Direct Voltage Reading Diagram
Section 3.1 of the Donner 3500 manual. Using the Donner 3500 as a voltage meter. Click image for larger view.

Donner 3500 plugboard for voltage readings
Plugboard set to match the direct voltage reading schemtic. On the other end, an un-regulated 12V power supply is feeding into the circuit to be metered. Click image for larger view.

Donner 3500 meter reading result of voltage test
The meter correctly shows approximately 12 volts. Click image for larger view.

So far power up and voltage test return encouraging results.