IBM 3420 Magnetic Tape Drives

Certainly the heftiest items in my collection, I have acquired a set of 3 IBM 3420 tape drives. These massive tape drives, at 800 lbs each, were a staple of the IBM 370 generation of computers. but will also connect to an IBM 360 Bus-and-Tag Channel. I also got the IBM 3803 controller that you need to run the tape drives. The 3803 is as big as a drive, and consists of two computers back to back: one side talks to the Bus and Tag channel, the other side talks to a maximum of 8 tape drives.

Restoration so far has consisted of preliminary steps: cleaning, removing the deteriorating foam, acquiring bus-and-tag cables, IBM tape test equipment, finding the power connectors and the documentation, and getting a 3 phase converter (the tape need 3 phase power to operate). It has taken quite a long time to get there, but as of June 2021 we have the schematics for both the tapes and the controller.

Video Series

I bought myself a few magnificent IBM 9-track tape drive. These are from the IBM 370 era, but will also connect to an IBM 360 Bus-and-Tag Channel. I also got the IBM 3803 controller that you need to run the tape drives.


We have been able to acquire good documentation on the tape drives and the controller. My tape drives came with their "ALD" or Automated Logic Diagrams. These are the IBM schematics. A Patreon of the channel put me in touch with a fellow named Gabriel Nielson that had the ALDs for the 3803, and a lot of maintenance manuals. Between both of us, we have enough of a set that we should be able to do component level repair of the system.

Power Connectors

Finding the tape power connectors for the 3-phase AC input got me mystified for quite a while. They are unusual square connectors with large lugs, and they go from the tapes to the 3803 controller. The 3083 controller in turn has a single power cable with a giant but completely standard 3 phase power plug. But eventually, Ignacio Menendez, a volunteer at the Computer History Museum and former IBM CE, put me in touch with another former CE who still had one of these cables, which he actually wanted repaired. He sent me the cable, and from the markings on the connector I was finally able to establish that the connectors were from the AMP G-Series of modular connectors.

They were still pretty hard to find, but I was eventually able to gather from eBay some shells, some female contacts, some male contacts, and some inserts. The shells will have to be slightly machined to work with the keying, and I will have to re-machine some inserts, but I have an example male and female inserts I can copy, and enough contacts to populate the connectors.

Here are the 8 female power connectors on the 8303 controller:

Here is the male connector on the tape drive:

Here is an original cable, part number IBM 2523073. This picture is from one in the Computer History Museum collection:

Here are the exact connector part references I was able to infer. It takes many parts to make one connector.

AMP G-Series with type XII contacts


  • Receptacle Socket: 202279-3 or -4

  • Plug: 202275-3 or -4 or 202786-1 or -6

Cable backshells

  • 202764-1 (same for plug and receptacle)

Contact Inserts:

  • female AMP G-SERIES 202625-2

  • male 202624-2

Type XII contacts

  • Smaller guage wire: (16, 14, 12), male: 66261-1 (also -2 and -4), 66262 grounding, also strips 66255-1 (-2, -4, -5, -6, -7, -8) and 66256 grounding

  • Smaller guage wire, female: 66740-2 (-6 and -8), strips 66740-1 (-5 and -7)

  • Large gauge wire (10), male: 66259-1 (-2 and -4), 66260 grounding, also strips 66253-1 (-2 and -4), 66254 grounding

  • Large gauge wire (10), female: 66741-2 (-6 and -8), strips 66741-1 (-5 and -7)

Power cable

This info is from my examination of an IBM 2523073 cable assembly

Power cable is exterior diameter 0.55. It has 5 wires in it, not sure why (only 4 are needed). Wire gauge measures at 2.32mm, which gauge 11, quite inconveniently in-between the standard 10 and 12.

  • Gauge 10 = 2.58mm

  • Gauge 11 = 2.30mm (IBM original assembly)

  • Gauge 12 = 2.05mm

I believe gauge 12 should do for a short cable run. These are available today as:

  • SJOOW portable cord (300V rated) has ext dia of 0.48" bit too small

  • SOOW portable cord (600V rated) has ext dia of 0.65" too big

Here is the documentation on the G-series AMP connector