After several years of looking I Found some more of these to offer to you. You are looking at transformers removed from Scientific Atlanta 15 kHz audio cards. These cards were produced in the late 70's and early 1980 and these transformers made by Jensen under a "house number" for S-A. These are excellent 1:1 line transformers. It is reported that they are the same specifications as the current Jensen JT-123-BLCF with a few differences. The transformers are nickel-steel and have only four leads because it was made as a 600:600 matching / isolation transformer. These transformers are capable of a flat frequency resp from 20Hz to 150KHz, I have seen some claim an even wider range, but I have not made my own measurements. Deviation from linear phase (DLP); 20Hz to 20KHz at +4dBu test signal is typically +0.3/0 degrees and a Max of +/1 degree. Distortion at 1KHz, +4dBM drive is <0.001% and at 20KHz, same drive level, is 0.016%. Max output level is a min of +26dBu and a Max of +28dBu. CMRR is 110dB @ 60Hz and at 3KHz, Min of 65dB and a Max of 75dB. These are impressive specs. If you need line isolation these are your answer. I am selling these in pairs as removed from the cards. Appearance may vary SLIGHTLY. Some of the insulator color varies. And some minor marks on the paper from storage on one set.