Originally posted by dR-Green
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After measuring out the wire, (66.2 meters) I constructed the first version Extracoil following the ‘Tentative Extracoil’ calculation formula. I found that for my spiral coil the extra coil inductance was too large, and the frequency of it too low to resonate compared to that of the spiral coil (and adding any capacitance will bring it down even further). Unwinding it some then made the length to height ratio incorrect. - I noticed that this maybe why you recently added the variable air capacitor across the secondary coil on your rig, as to bring down the secondary frequency to match the Extracoil’ s frequency better?
Yeah, I would agree that measuring out the wire may be unnecessary. I do it because then I can measure out two identical wire lengths, (side by side), then I know for sure they are both the same length and it’s a physical measurement conformation to the calculated length by the number of turns method.
Having said that, I unwound the Extracoil and started again, this time using a larger diameter wire and larger space (length by calculation this time). Amazingly, this time the self-resonant frequency of the (new) extra coil is almost exactly the same as the spiral coil self resonant frequency. 2.08Mc V 2.085Mc, however the Extracoil is over 57% longer in wire length with a 1:1 H x L ratio. So I’m happy to work with that for now, as I’ll be trying for a capacitive coupling link between them, not directly connected as Eric highlights.
As for lighting bulbs: I have bought some ‘vintage style bulbs’, not really vintage, but copies of, which are 25W bulbs but they have long fine filaments and a large vacuum space. All of these bulbs light quite nicely. The small 25watt bulb shown in my previous picture, when I push my amp to full power, the light from that bulb is something to behold, it is @#$! blinding! Extremely bright.
I’ll have to give the plate and hand trick a go too, which sounds like some fun. - I’ll continue to play with adding the extra coil to my rig and see what happens with that.
Pictures of the ‘vintage’ bulbs, Extracoil, with some statistics and results to come later.
Sputins.
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