<html><head></head><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px"><div id="yui_3_16_0_ym19_1_1481063715593_11964">All,</div><div id="yui_3_16_0_ym19_1_1481063715593_11964" dir="ltr">I'm looking at the output transformer. At 50 volts you would need 16uH so at 12V it is down around 4uH. Changing from a type 61 core to type 43 core the permeability is about 7 times higher. That should yield enough reactance. BN 43 7051 or the Fair Rite equivalent should work at 12 volts. I measured the inductance of 1 turn at around 8uH. I had them in my big amplifier for a while and 2 turns primary worked fine at 50 volts on 160 meters. I only changed them out for mechanical reasons. BTW I'm using type 43 material on 6 meters with no heating issues but my flux density is under 10g. </div><div id="yui_3_16_0_ym19_1_1481063715593_11964" dir="ltr">Frank,</div><div id="yui_3_16_0_ym19_1_1481063715593_11964" dir="ltr">WA1GFZ</div></div></body></html>