Found this, at the bottom is an OPT for 811's. 350W 1500V rating.
http://www.vt4c.com/shop/program/main.php?cat_id=112&group_id=7&hit_cat=These control transformers have a 4000VAC hi-pot rating. Might be good for modulation, especially cathode mod.
http://www.mci-tran.com/C49.htmlhttps://www.edcorusa.com/ampoutputThis one has transformers to match speaker to line. They have line voltages not only 25 and 70V but also up to 140V, which is enough to drive 3-500Z grids, which require 100-150V per grid at high current and are not easily matched by the usual modulation driver transformers designed for high-Z tubes like the 304TH, 810. I have not tried these, just saw them.
