Let's use that DRRI as an example. Put the PT on the bench. There are 10 wires. We're gonna measure resistance between wires. Pick any wire and connect one meter lead to that wire. Now check resistance between that wire and ALL the remaining wires. Make notes about any wires that measure any resistance. Twist all wires together that show resistance readings. This will be a winding.
Now pick another free wire and connect one meter lead to that wire. Now check resistance between that wire and ALL the remaining free wires. Make notes about any wires that measure any resistance. Twist all wires together that show resistance readings. This will be another winding.
Repeat this procedure until you have all wires grouped. There should be no single free wires. For the DRRI PT you should end up with 2 black wires in one group, 2 yellow wires in another group, two green wires in a third group, and 2 reds, one red/yellow, and one red/blue in a fourth group.
Black (or black and white) is typically primary winding. Yellow is typically 5VAC filament winding. Green is typically 6.3VAC filament winding. And reds are typically high voltage winding with red yellow being a center tap and red/blue being a bias tap.
You can confirm that you got it mapped out correctly by looking at the schematic available in Hoffman's schematic library. (Click link below this message.)
Apply what you learned in this exercise to your other unknown transformers. I could probably write a 10 page essay on this topic, much of which comes from training and real world experience. But you have enough info to get started. And you can always ask questions about a specific transformer, posting pics of course.
Topic: Hoffman Stout Transformers Question (Read 2854 times)