JW
Well-known member
I have 4 of these little square can, shielded mic input transformers from an old busted Altec 1674. I'm building a buddy an API preamp for Xmas. I was wondering if they look okay for an API 312 input?
The only info I can find about them is briefly mentioned here: https://groupdiy.com/index.php?topic=44710.20 where BruceO says: "Altec 1674 1678 1684 automatic mic mixers have some marked ALTEC/671-1323/651-8957 in them, square Mu Metal can, center tapped, 1:4 and 1:8 ratios. Tested pretty good, well shielded. These mixers also have a line output transformer in them (in the case of the 167x it is the same size as the api output trafo's I have not tried it though).
"
The primaries are in series coming out of the transformer. But I unpotted one, and inside I was able to seperate the center tap and I believe I can now wire the primary in parallel like API.
I'm having a hard time getting dcr readings. Maybe my dmm
But I have been able to measure 24 ohms between the top and bottom windings (with series wiring,) on the primary side. On the secondary (also series wiring) I was able to measure 1.3K between the top winding and the center tap. The bottom winding was connected to the case and didn't seem to get any continuity with other windings.
Does this calculate to a 1:8 transformer if I wire the primaries in parallel and leave the secondaries in series?
I attached a screen shot of the Altec schematic input, the best I could find. I'm able to read a 200K termination resistor.
The only info I can find about them is briefly mentioned here: https://groupdiy.com/index.php?topic=44710.20 where BruceO says: "Altec 1674 1678 1684 automatic mic mixers have some marked ALTEC/671-1323/651-8957 in them, square Mu Metal can, center tapped, 1:4 and 1:8 ratios. Tested pretty good, well shielded. These mixers also have a line output transformer in them (in the case of the 167x it is the same size as the api output trafo's I have not tried it though).
"
The primaries are in series coming out of the transformer. But I unpotted one, and inside I was able to seperate the center tap and I believe I can now wire the primary in parallel like API.
I'm having a hard time getting dcr readings. Maybe my dmm
But I have been able to measure 24 ohms between the top and bottom windings (with series wiring,) on the primary side. On the secondary (also series wiring) I was able to measure 1.3K between the top winding and the center tap. The bottom winding was connected to the case and didn't seem to get any continuity with other windings.
Does this calculate to a 1:8 transformer if I wire the primaries in parallel and leave the secondaries in series?
I attached a screen shot of the Altec schematic input, the best I could find. I'm able to read a 200K termination resistor.