[Elecraft] High Current On TX

Sun Jan 26 10:47:00 2003

a) 2.6 A is fine. You probably have your Current Limit menu item set to 2.5.
Good for batteries, bad for running 15W.

b) The alignment between the transistors and the heatsink is not cast in
stone by the machining (which I do not doubt). The transistor leads are bent
by the builder 90 degrees. There is a great deal of leeway in where you can
make the bend and have the leads go through the circuit board holes, but
very little and have the mounting hardware align.

Without rereading the manual, I'd guess they just say bend them. Maybe we
should suggest they say to bend them, then test fit the mounting holes AND
THE THREE LEADS, (on the bottom of the board - that's more accessable), and
get it right before applying heat.

For your case, if necessary, desolder and rebend. However, if it's only a mm
or so, you may be able to drag the transistor into position. I don't know
how tough they are, so if you pull a lead out of it, don't write to me,
write to parts!

Stick a drift through the board and transistor, lift the transistor from the
board about 2mm, and pry the transistor in the correct direction (Good luck,
and be careful).

It may be you are missaligned on one of the 2-d fasteners. If so, disregard
all the above. The 2-d fasteners have a deep and shallow side. You probably
have one backwards.

If you REALLY think you have a miss-machined bottom case, I'll measure mine.
Odds are, they match.

Dan / WG4S / K2 #2456

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Mike Lewis
Sent: Sunday, January 26, 2003 4:31 AM
To: [email protected]
Cc: [email protected]; Skip Cubbedge
Subject: [Elecraft] High Current On TX

Hi Everyone,

I apologize in advance for this topic - must have been covered in MANY
previous posts. If anyone has an archive reference in addition to/instead of
any direct comments, that would be great.

Just finished my basic K2 this evening (Saturday night, about 9:00 pm or
so). and have been calibrating/tinkering/troubleshooting with it since then.
Things seem to be basically ok. The receiver appears to work on all bands
(although the only band that is open that I have an antenna for atm is 40m),
and the transmitter puts out at least 10w on all bands after going through
the setups. I do have TX current that is a bit in excess of spec though. I
have tried to stay away from any of the higher TX powers for any length of
time, and have refrained from really doing anything other than listening, or
some of the very prelim checks. I made some measurements, using the rig's
readouts, and going through a Diawa cross needle SWR meter also reading
power on the 15w scale. values slowly climb while in tune mode (this is
normal?), so readings given are at initial key down.

K2 Power Setting (W)  Diawa Power Reading(W)  K2 Current Reading (A)
1.0                   ~1.5                    0.96
2.0                   ~2.4                    1.22
5.0                   ~5.25                   1.58
10.0                  ~10.0                   2.08
12.0                  ~11.75                  2.28
15.2 (Max setting)    ~13.0                   2.60 (was high current)

An additional problem was that the holes in the heatsink did not quite line
up correctly, and I was unable to put in both of the screws holding the
heatsink to the K2 RF board mounting block that is located right near the
finals. For this reason, I was very ginger about applying any significant
power for any significant time, figuring I might have a less-than-optimal
thermal resistance for the finals. Not sure why the misalignment. Everything
up to now has been so perfectly lined up, I stopped even thinking about
these type of problems.

Questions are:

1) There must be some likely culprits for this type of an over-current
problem, given that the rig seems to basically work. Any ideas on where to
look, how to proceed?

2) I am at a bit of a loss to understand the misalignment of the case
pieces. Of course the mount block is underneath the binocular T4
transformer - UGH - I really don't want to have to pull that off if at all
possible. I can't see that that is the problem , but what else is there to
suspect, other than a mis-drilled case piece? Is drilling the hole a bit
bigger in the heatsink piece a viable option? The misalignment is not
severe, just enough to make the screw go in 'cocked'...

Thanks,

73 de 'MF/ML

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