IBM 4331 Mainframe

Jon Elson elson at
Mon May 1 10:46:04 CDT 2017

On 05/01/2017 07:42 AM, Paul Koning via cctalk wrote:
>> On May 1, 2017, at 12:38 AM, Guy Sotomayor Jr via cctalk <cctalk at> wrote:
>> Just to let folks know that I finally moved the IBM 4331 Mainframe this past weekend
>> from where it was currently stored to my shop.  Pictures are here:
>> <>
>> As can be seen in the pictures, it filled a 26’ box truck that I had rented for this purpose.
>> Right now I just have it placed somewhat in my shop.  Some early tasks will be:
>>    * I have to verify that I have everything.  Even if I missed some items, they won’t be
>>      scrapped.  I just need to go over what is currently in my shop and verify that I didn’t
>>      leave anything behind.  I’m mostly worried about cables at this point.
>>   * I have to figure out some way to produce enough “clean” 3-phase power to run the
>>     peripherals (the CPU is 220v single phase) as I only have 220v single phase coming
>>     into my shop.
> What do they use 3-phase for?  Motors?  I remember disk drives with 3 phase motors.  If so, a VFD is a good low cost solution since those are specifically designed for driving motors.
Some of the larger load devices may use actual 3-phase power 
supplies.  So, the 3-phase power either runs through a 
3-phase transformer, or is rectified and run through a 
switching converter to make the DC power.  These could be 
pretty hard to reconfigure to run off single-phase power.  
(The IBM 360's use a "converter-inverter" that rectified the 
3-phase 208V power to 300 V DC, and then inverted it to 
regulated 120 V 2.5KHz single-phase AC for the various power 
supplies.)  Not sure if any of Guy's equipment use a similar 
scheme.  The 2821 unit record control does use a LOT of 
power to run the 1403 printer.


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