API 2503 OPT
« on: January 08, 2019, 05:09:46 AM »
used in the 312 preamp and others, this has been covered many times, but here is a fresh print.  No tear down pics, but not a lot to see, a bunch of twisted wire on a nylon bobbin,

this is a prime candidate for first time DIY winders, as it has just one start and one stop, no insulation or interweaving, does not even need varnish,  and a very cool project as you can buy 312 PC boards and almost make it a complete DIY fab,  save the input transformer.

there have been several versions of this transformer, some with twisted wire, some not, some with 300 turns of #30, some with 287 turns of #29 ,  Jensen makes a version, as well as a few other people.

This transformer concept is also use on the Quad Eight OPT.

all the parts for this transformer can be bought from Edcor,  you can get more options for wire from evilbay, that way you can buy just enough for the job. Buy a small spool of red and a small spool of green.

Frequency response is flat to 1 megahertz, if you discount the massive phase shifts that go on during the transition from linkage from the core to the linkage by way of inter-winding capacitance .

You can measure the capacitance of the winds with a standard DMM with a cap checker.  It should be well into the Nanofarad region.

Do not worry about getting the exact twists per inch on the wire, 2 to 3 twists should be fine.

upload folder is full, but we have it loaded onto this site>  :D


direct link>

« Last Edit: January 08, 2019, 05:18:27 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
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Re: API 2503 OPT
« Reply #1 on: January 09, 2019, 04:03:33 AM »
Very nice

Thanx CJ
I ping therefore I am


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