OCFMasters spent two years delving into the ins and outs of End Fed antennas. Throughout that time, we discovered that most End Fed antenna transformers used higher impedance transformations than necessary and were wound in a way that limited the high frequency response of the transformer.
We also found that applying the capacitive loading technique we applied to OCFs and 40M dipoles worked very well on End Fed Antennas with low SWR on all bands depending on the power rating of the matching transformer where the high-power transformers with multiple cores had losses that precluded operation on 6M. The most important thing we learned to make them work consistently on all bands was the need for a properly sized counterpoise as shown in the diagrams below. Our 36:1 transformer and 1:1 Balun/Chokes work well on this antenna. Antenna wire is #14 Flex Weave or THHN from Hardware or Electrical stores.