The Dukane 3A55 is a vintage balanced line transformer for matching a low impedance line input source (like a microphone) to an amplifier.
The internal workings of the 3A55 have been something of a mystery, so I decided to take one apart. I had one with broken pins, and in order to repair it I had to take it completely apart.
The 3A55 looks like this, before dismantlement:
The cover of the 3A55 is made of Mu metal for isolation, and it is crimped onto the base. I removed the cover and found the whole thing was potted with some kind of black goo.
I heated the assembly in order to make the goo easier to remove. There was a lot of it:
After a while I was able to extricate the little transformer and wiring. Here it is, with wires attached to the octal base:
From here I was able to create a schematic of the 3A55:
This is helpful for those who want to employ a 3A55 but don’t know the details of the octal pinout.
This transformer is popular in vintage PA and other amps, and it is known for excellent performance.
