DEC Pulse Transformers

In 2004, I obtained a data sheet with manufacturing instructions for the T2037 pulse transformer. Pulse transformers are used in a variety of Gxxx modules, for instance to form the pulses to read/write core memory.

There are several alternate part numbers for the ferrite toroid there, but the "modern" equivalent is the FT-37-77. The "37" refers to the 0.37" outside diameter of the toroid. The "77" refers to the material formulation of the ferrite (material "72" has the same magnetic properties). (As of this writing, FT-37-77 toroids can be affordably obtained here.)

Essentially, 16 turn and 7 turn windings of color coded #33 wire are equally spaced on the toroid, and the result is soldered to the posts of the carrier. The carrier is a round cup with a 9/16" outside diameter and a height of 5/16", which is then filled with (black) potting compound.

Recently (April 2017) I had an opportunity to look into the T2052 pulse transformer. Like the T2037, it is used in core memory circuitry, and like the T2037, it appears to be constructed on an FT-37-77 equivalent toroid. Here is an email I sent to Josh, detailing my findings.

The main difference is that it appears to be wound 1:1, with each coil having 25 turns. It isn't clear what wire was used. Cosmetically, the T2052 has an orange potting compound instead of the black, making it easy to keep them straight.

Particularly in older PDP-8 models, instead of a proper carrier, the coil was placed with leads extending through a small circular PCB, and the result was apparently dipped in a brick-colored potting compound. This process results in a "gumdrop" appearance of the result, which is then stenciled with the last two digits of the transformer's type ("52", etc.). Unfortunately, the leads are not strong enough not to flex when the cards are vibrated, which sometimes leads to metal fatigue, and they can become disconnected (or even fall off the boards entirely).

Here are some photos:

Newer style of pulse transformers.

Partially disassembled "gumdrop" T2052.

Last updated on 05/9/17 04:01