I have a Jennings UCS-500. I'd rather use it for something else, but I
agree its suitable.
Coil inductances range from about 3uH to 6uH. Air wound is appropriate
as dissipation in the coil will be around 15W at legal limit assuming
unloaded Q of 200. I'm afraid that would melt the plastic ribs on even
the heavy-duty B&W/AirDux TL type coils. But big air wound coils take up
space. I'd like to keep the enclosure small. It would be nice to fit it
all in an inexpensive off the shelf PVC weatherproof electrical box from
the big box store. Which also argues against using that big vacuum
variable and motor.
--
Art Greenberg
art@artg.tv
On Mon, Aug 14, 2017, at 09:31, Jim Thomson wrote:
> ## Id use motor driven vac caps myself..and be done with it.
> Plan B would be to use motor driven air variables. They will easily
> handle the peak V and average currents involved. Use relays to
> tap the single coil. Like a DPST, with all contacts in parallel..which
> will double the current rating, and quadruple the power rating.
>
> ## use some BIG wire for the hb coil, like 8 ga. The entire mess has to
> be in a waterproof box. Put a couple of metal finned resistors in there
> to keep it warm, and dry. Then add some silica gel powder in there too, to
> absorb any moisture. The problem with air variables is the sliding
> contacts on the rotor assy.
>
> ## A motor driven roller coil will probably give you grief....eventually.
> All depends on the type of contacts used.
>
> ## Vac caps typ have unloaded Qs of 5000. Coils are typ 200-2000
> depending on construction. 8 gauge wire = .128 which is essentially
> the same as .125 tubing. .1875 tubing will also work. How much
> inductance is required ?? Since this is just a 80 +40m affair, you can
> get away with large diam coils, which saves length. .1875 and .25
> tubing typ comes in 15 + 25 + 50 foot rolls. Then it will freestand
> in air.
>
> Jim VE7RF
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