I always wondered what is really the output Impedance of the LF339...? The manufacturer on your website did not specify this clearly, as we know for OTL's, parameters like internal output impedance is very important and is worth to know it, there is No transformer to match the impedance of the load, so to satisfy my curiosity I guess not only my, finally found some time to do some measurements.
Summing up and given the fact that the amp does not have a negative feedback the output impedance of our amplifiers is satisfactorily low. Of course! it depends largely on the type of tubes which we will use on output, no doubt TS5998 have the lowest in mid rage about 23 Ohm and about 29 ohm at very low end 20Hz and right behind her are 7236TS & Cetron all can work without fear with the 32 Ohm Grado family. But even Chinese 6N13PJ is not too bad with the average impedance about 38.5 Ohm and peak about 43 Ohm at 20Hz, no problem they will fit with the 50 Ohm and Up cans.
Edited by WALL-E - 10/8/13 at 1:17pm