|[AMRadio] National Knob|
k4kyv at charter.net
Tue Feb 13 02:32:00 EST 2007
>Does anyone happen to have a National catalog with their vernier tuning
>mechanisms in it? I need the number of the 3" National Velvet vernier
>knob and assembly. I actually need the product, but they seem to be
>very scarce. I just happen to think, maybe it's in an old Handbook!
The original velvet vernier was black bakelite. It had 0-100 scale, and
looked very similar to the old bakelite dials on 1920's broadcast radios,
except that it has the planetary drive mechanism. That was known as the
"Type A" dial. It came in two sizes, one about 4" in diameter, and a
smaller size about 3" in diameter.
After WW2 it was replaced with the type AM dial (type A - Metal). The
planetary mechanism is identical, but the dial skirt is bright metal instead
of black bakelite. It only comes in one size, about 3" in diameter.
They also made a variation with a real vernier scale on it, like the scale
on a vernier caliper. This allowed precise setting of the dial for
frequency meters and similar applications.
There is also a Type B Velvet Vernier, which has a small peep-hole scale and
a smaller tuning knob, as well as a variable reduction ratio. These look
similar to another type of early broadcast receiver dial. These use a
friction drive against a small wheel, instead of the planetary drive
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