got a schematic for an amplifier.What is:
an Unelco
a coil with 3 turns #16 enameled wire,3/16" ID (everything unclear except
the 3 turns)
dura mica


I'm not sure if Unelco refers to a brand name, or if it is a type of
construction unique to a certain brand. But whenever I run into Unelco
caps, they are always these 'square pads' that have a tab on the side.
The capacitance is from the construction. The square pad is soldered
down, and the tab is insulated from the square tab, the insulation being
the diaelectric. You usually find these in high power amplifiers as
bypass on the final stages where there may be respectable RF current.

As to the coil, there's usually one other 'spec' that you seem to be
missing. That's the 'turns per inch'. But in it's absence, you can
still easily make the coil. In this case, just get a 3/16" bar and wrap
your 16ga wire around it 3 times and you have your coil. If it's not
specified, try to make the coils spaced 1 width apart. Some people
wrap TWO wires to make the coil, then unwrap one, leaving space
for a wire between the wraps.

With 16ga wire it's not easy, but if you can find a 'coarse thread bolt'
in 3/8" diameter, wrap the wire to follow the threads. Then unscrew
the bolt out of the coil. If you need wider spacing, you can gently
'pull' the thing to stretch it out. I had one kit one time that specified
the coils by what bolts to wind them on...