[R-390] That R-390A "BFO Thingy"

[Barry Hauser]

Bob wrote:
> They are ALL 1:1. They were built for multi-turn pots which were therefore
> built-in verniers over the single turn variety. They all mount to the
front
> panel nut.

Hi Bob:

Well, I think you're right on the small scope type verniers.  Newark lists a
bunch of them.  Here's one:

http://www.newark.com/NewarkWebCommerce/newark/en_US/support/catalog/product
Detail.jsp?id=12F4498

-- 15 turns, but as I recall, I've always seen those coupled to a multiturn
pot as you point out.  The business end turns 15 times around, or 11 for the
other models.

But -- never say "ALL". ;-)

There is a similar style, but larger -- 1.5 to 2 inches in diameter which
are true verniers with reduction.  Mouser lists 3 of them.  Here's the link
to the pdf page:

http://www.mouser.com//index.cfm?handler=fra_pdfset&dir=612&pdffile=665

These appear to be of the same style as the ones Radio Shack used to carry.
I may have one or two lying around somewhere.  They provide an 8 to 1 gear
reduction.  However, they mount up not by the front panel nut, but
flush-mount with 3 screws.  They take a 1/4" shaft, but have a coupling with
(as I recall) a round head screw rather than a setscrew, so may need an
oversized hole to clear.  Not sure how much play is available on the depth.
One possibility to avoid drilling 3 holes (arghhhh!) is to use 3M mounting
tape.  That's the stuff that's sticky on both sides, thick and rubbery.  It
will hold for sure, but when the time comes to remove it, it will probably
take the paint with it.  I seem to recall these having a rotation of 270
degrees, roughly matching a typical pot.  However, the Mouser description
says "calibrated for 180 degrees rotation" -- which should be good for the
BFO anyway.

The last type I mentioned in my previous post was truly a gear reduction
drive, but I haven't found a listing for it.  These were simply a knob
shaft, a drive shaft and a disk shaped "gearbox" in the middle. (might have
been a friction drive)  No knob, no scale.  Not sure how it mounted.  Used
to be in all the major catalogs in the old days.  Anybody familiar with
those?

Barry