"Leon Heller" wrote in message ...
"Tim Wescott" wrote in message
...
Leon Heller wrote:
"Gregg" wrote in message
news:t4eld.149312$df2.42254@edtnps89...

I stumbled across a few at surplus outlets, I'll see if I can dig up
URL's. $50 to $150 USD, depending on KW rating.

You can build your own fairly simple though, for a lot less :-)


An old-timer I used to know made his own from plastic drain pipe. He used
a lathe for cutting a spiral grove in the pipe for the wire, and machined
most of the other parts himself.

73, Leon
I'm not sure I'd qualify anything requiring a machine lathe as being
"simple".

It is if one has a lathe. 8-)

Strictly speaking, he wasn't making roller inductors, anyway, as the contact
was moving across the turns giving one turn resolution, like a rheostat. He
only used QRP. Making a proper roller inductor for high power like those
made by Henry would be quite difficult.

73, Leon


Difficult indeed!

I worked at Barker & Williamson during the early 60s when they were
still making these things. First of all, you have to go out and
located silver plated bare wire for the coils. Then you're going to
have to machine yourself a precision roller that also needs to be
silver plated, and a silver plated rod to carry the roller with as
little lateral friction as possible.

The balance is comparatively simple, if you have a source for G7 or
G10 material to fabricate the frame, and are comfortable in machining
fiberglass-epoxy laminates to a reasonable degree of precision. (B&W
of course used custom molded and glazed ceramics, not laminated
fiberblass, but that is simply a nit!

I personally wouldn't want to even attempt it. Far cheaper to buy a
surplus variable inductor.

Harry C.