An old 'rule of thumb' for link coupled tuners is the coil should tune with
about 1 pF of capacity for every metre of wavelength. This gives the ability to
get up to about 5000 ohms with a reasonable working Q. For wire size, I'd use
the numbers from the tables in the older ARRL handbooks, but I get away with
about 12AWG - but I don't run 1500 watts. The link coil feed from the
transmitter should be big enough to handle around 5 to 6 amps of RF at full
legal power, which suggests about 10AWG on the LF bands, and 8 AWG on the
higher bands, or similar size tube. But you'll get away with a bit less if
you're not running full pwoer RTTY or SSTV or similar.
I find that too small a link winding is a problem, and I'd use more turns than
you'd guess, with a series tuning capacitor. Too big, and you get otehr
problems like the series cap flashes over! I use enough link to series
resonate with 1000pF on 80, 500pF on 40 (same size link in my case) and 500pF
on 30, with 750volt rated caps for series tuning.
Hope this helps.
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