On Nov 13, 9:26�am, Ross Tucker wrote:
I am almost ready to begin fabrication of a new transmitter that I
have been working on for a long time now. However, one detail is still
eluding me- I would like to use a single rotary switch to select taps
on two different coils. In-line ganged switching would be inconvenient
for my layout. Is it possible to homebrew a mechanical linkage to turn
two switches? I have a front panel and metal deck (vacuum tube
construction style), so I could mount gears and cams and stuff, and my
layout does have a good clear space between the coils, so there is
room. My problem is that I have never read anything about doing this
and don't know where to begin looking for parts, etc. Again, I have
two coils with four taps each for 40, 20, 15, 10m.

A standard way of extending rotary switches 40+ years ago (notably
the Centralab types) was to use a quarter-inch rod coupled to two
separate switch shafts. Centralab style had flatted shafts to index
their
switch wafers. A shaft extender could be used with the rounded rod.
All of
those hardware pieces are still available at distributors such as
Jameco or
Ocean State Electronics. Rotary switch pieces, per se, aren't
available now.

As a suggestion of a different way, relays are good ways to 'remote'
the
switching. Modern automobiles use quite a few relays and small, low-
power
coils with high-power contacts are plentiful. Relays are common in
automatic
antenna tuners. Four taps selected on two coils would need two sets
of
SPDT to DPDT contact arrangements. See Futurlec or Digidey or Allied
or Mouser for such relays. There is a fairly wide range of relay coil
voltages available and each relay is less than $5 in small
quantities. Usual breakdown voltage ratings are about 250 V so it is
no sweat to handle 100 W transmitter
power outputs.

For all-mechanical contact coupling, I might suggest 'tactile' snap-
action switches (familiar name 'Microswitch') which are plentiful
now. Mechanical
coupling could be cams or sliding bars with cam surfaces on them,
switches
in-line. Sliding bars can be made from aluminum stock found at most
do-it-
yourself home repair stores. I did something like that a dozen years
ago
using aluminum right-angle stock, making cam surfaces by cutting down
the
aluminum slightly to leave the original edge as the 'cam.' The kind
of tactile
switches depends on their contact rating and what kind of RF power you
are
handling. Most on the market today can't handle much more than around
20 W.

Good luck on your project!
73, Len AF6AY