In article ,
Ashhar Farhan wrote:
let me explain this a little more visually.
to begin with, i imagine that you are building this ugly style over a
copper clad board. Now, imagine that you have soldered another piece
of copper clad board (about an inch high and 2 inches across) so that
stands vertically at ninety degrees from the base board.
Now imagine that you have cut out a small mouse hole in this 'wall'.
The size of the mouse hole is just enough to let the FET's body (and
not the leads) pass through.
You take an FET, bend its drain and source to ninety degrees and away
from the FET body. Now you slide the FET into the mouse hole. Bend
down the gate and solder it to the base copper clad board.The source
and drain leads should be on either sides of this wall (the sheild).
this will prevent the source and drain from coupling the energy back
to each other.
A slight variation on this approach, which I've seen recommended for
use with U310 (TO-52 metal case) is to actually drill a small hole
downwards through the "ugly-style" copperclad, just barely large
enough to admit the body of the JFET. Drop the JFET into the hole -
it's fine if the metal case contacts the copper, as the case and gate
are connected together. Bend the source and drain out sidewise, leave
the gate lead sticking up in the air, put the shielding piece of
copperclad with the "mouse hole" into place, solder it to the board,
and then solder the gate lead to the copperclad on one side of the
shield.
This results in a very short, low-inductance connection of the gate to
ground.
This technique would probably work just about as well with a J310 or
similar TO-92 plastic-package JFET, although it won't give the
additional benefit of grounding/shielding via the metal case.
As to the U310 - anyone know of a convenient source? I haven't seen
anyone selling old-stock U310s on the Net, and there's only one
manufacturer I know of making them (Linear Systems).
--
Dave Platt AE6EO
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