[Elecraft] Power for KAT100

[Rich Lentz]

 > Thought I might try it any way since there is voltage there and the
KAT100 probably doesn't take much current. =20

The reason you measure voltage there is that the diode has a relative =
low
resistance compared to the ohms-per-volt rating of most digital =
voltmeters
(These have very high ohms-per-volt rating approaching that of a VTVM
(Vacuum tube voltmeter or these FET input voltmeter.)  With the high =
input
resistance very little current is drawn thus very little ( ~ none) is
dropped across the diode even though it is reverse biased.


 > Or, I suppose you could bypass the diode, perhaps raising some risk, =
but
I don't know what it would be.  If I get adventursome, I will post the
result.

That would be quite risky as you not only create the chance of inputting
reverse voltage at a fairly high current ( no reversed biased diode to
prevent it) and risk the chance of relying on the fuse (RGE300) to =
protect
your K2, you also introduce the chance of causing problems by shorting =
out
the power and burning up PCB traces, the wire from the KPA100, etc. =20

I have several pieces of equipment that use the same connector as the K2 =
and
need 13.8 +/- DC center positive, voltage.  Thus, I have several cables
wired up to a decent power supply.  While testing my newly built K1, I
disconnected the cable from the K1, and layed it on the desk.  The =
center
conductor of the plug on the cable I disconnected sticks out ever so
slightly, and in moving the K1 around the center conductor touched the =
shell
of the BNC for the antenna.  In very short order (Instantaneously) a =
PASS
transistor, the fuse, and the AC thermal overload were all popped on the =
PS.
It was easy to reset the overload and replace the fuse, but not to =
replace
the pass transistor.  Think of this current going through your K2 via =
the RF
board to the KPA100 to the power supply.  Some of the fuses may help but
which ones?   I now disconnect the cable from the PS before I disconnect
from the RIG.

Rich
KE0X