[Elecraft] Re: One of my 2SC1969s keeps overheating...

[Ron D'Eau Claire]

Those are excellent points about being absolutely clear when it comes to =
the
order of hardware, John.

As a rule, the function of a lock washer is to keep either the nut or =
screw
from turning due to vibration or other stress. The lock washer "digs in" =
to
the screw or nut and the solid material on the other side and keeps it =
from
turning.=20

A screw or bolt is actually a spring. When a nut and screw are =
tightened,
the screw stretches. Normally, the stretch is only a very tiny amount, =
but
it's enough to provide a LOT of friction between the screw head and nut =
and
the surfaces they bear on, and as long as the amount of stretch exceeds =
the
expansion due to heat in the worst case, they will remain tight. =20

(There's a fun demonstration about how important it is for a screw to
stretch and act like a spring to tighten a nut and bolt. It involves
freezing Mercury, which is NOT elastic, in molds the shape of a nut and =
bolt
and then mating and trying to tighten the pair. No matter how big of a
wrench is used to "tighten" the nut on the bolt, one can always loosen =
it
with a simple twist of the fingers (protected against the cold by =
suitable
gloves of course)).

When no nut is used, as in the case of the screws and 2D fasteners, the =
lock
washer is often placed under the head of the screw.

Ron AC7AC

-----Original Message-----
Subject: [Elecraft] Re: One of my 2SC1969s keeps overheating...

Hello Everyone.

...The reason the 2-D fastener is slightly higher than that of the
transistors is because the lockwashers associated with the 2-D
fasteners were mounted between the bottom of the RF board and
the fasteners.  However, according to some of the photos in
the back of the Owner's Manual, the washers are apparently
placed between the screw head and the TOP of the RF board.

In my defense, the instructions on Page 33 do not indicate
where the lockwashers need to be installed:

        "Secure each fastener from the top side of the board
         using two chassis screws and two #4 lock washers."=20

(I never thought a lock washer would be placed beneath a screw head,
but then again, I'm an electronics guy, not a mechanical guy.)

Removal of the 2-D fastener near the RF power amplifier circuitry
requires removal of T4.  All other fasteners should be fairly easy
to remove and re-install.

Mystery solved.  (Hopefully!)

*Sigh*


73, de John, KD2BD
K2/100 #3563