Okay so I tried 3 cores of the blue Arnold MPP cores, stacked together and
wound bifilar with 4-8 turns, I think 4 turned out to be the magic number
for flattest response....and it looked great, but the soak test failed...got
pretty hot after 5 minutes key down with 500W. So after a brief recovery
period for the dummy load, I tried the other large cores I have. I had 3 of
these, absolutely no markings, 2.4" OD and 1/2" thick...went for broke and
stacked all 3 of them, drop of CA between to hold them then wrapped with
Scotch glass tape. Wound my usual 12ga Teflon coated bifilar wound, again
starting with 7 turns per half and working down to where the response was
flattest..again it was 4 turns, but still at 1.1:1 at 30MHz, so I tried 3
and it dropped to 1.08:1 at 30MHz. Still flat down to 2MHz and with 3 turns
the bump is still 1.3:1 at 45MHz and then it drops back down to 1.1:1 up to
70MHz. Nice! So I tried the soak test and this time....woooo hoooo! She's
cool as a cucumber, well, a little warm, but I burned my fingers on the
dummy load so it definitely is working, and I think will be good for the
KT-34XA with my current setup. After the dummy cools, I will try the soak
test at 30MHz and see how it does. I have been testing at 14.250MHz.
So one final question, is it ultimately a balun design goal to have as few
turns possible on the core to get the desired results? I could go either 3
or 4 turns. The response is very similar for either.
Thanks all for your help and guidance. Much appreciated!
73
Paul
VE7KHz
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