K2/100 Fuse Holder Melting

[N4NAB John]

I was working CW at 50 watts and happen to look up and see a whiff of smoke on the rig end of the fuse holder. The rig never cutoff and the the meters on the Astron indicated normal current and voltage. I immediately killed the power.

The fuse holder was too hot to touch but I did disconnect it from the rig and the PS and took it over to the bench for inspection. The rig end was melted . Further inspection showed no elevated temps on the APP on the rig or the APP on the power cable.

After the holder cooled down I separated the fuse holder and dropped the glass fuse out. The cap on the rig end had separated fell out also when I removed the fuse and the end of the glass was black.

Concerned about the K2 and the power supply I connected an alternate power cable and every thing checked out with no signs of a problem.

I searched the reflector and found several similar cases and concluded the fuse holder was not making a good tight connection with the fuse as pointed out in other posts.

Rather than replace the holder with another glass type fuse I opted for a mini-blade fuse thinking it was a more positive connection/solution. I found a mini-blade holder at Radio Shack ( after not finding them at two auto supply stores) PN 270-1237 as well as the mini-blade fuses. I bought two and have installed one in each leg of the power cable.

I suggest Elecraft take a look at an alternate fusing for that KAT100 cable.

[Fred Townsend]

John the problems with this type of fuse (cartridge) and fuse holder are
legendary. The higher the current the bigger the problem. In the factory I
have seen entire lots of defective fuses and fuse holders. The problem is
made worse by soldering fluxes. If you must solder a fuse holder, be sure
that all of the flux residue is removed. Of course no clean fluxes (NOT
RECOMMENED by Elecraft) make the situation even worse. There is no
substitute for cleaning fuse holders, inside and outside.

FYI a defective fuse and fuse holder combination is defined as any fuse that
fails to open at its rated opening current and time period. Not as we
frequently say a bad fuse meaning a blown fuse.

73
Fred, AE6QL


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of N4NAB John
Sent: Wednesday, February 22, 2012 5:52 AM
To: [hidden email]
Subject: [Elecraft] K2/100 Fuse Holder Melting

I was working CW at 50 watts and happen to look up and see a whiff of smoke
on the rig end of the fuse holder. The rig never cutoff and the the meters
on the Astron indicated normal current and voltage. I immediately killed the
power.

The fuse holder was too hot to touch but I did disconnect it from the rig
and the PS and took it over to the bench for inspection. The rig end was
melted . Further inspection showed no elevated temps on the APP on the rig
or the APP on the power cable.

After the holder cooled down I separated the fuse holder and dropped the
glass fuse out. The cap on the rig end had separated fell out also when I
removed the fuse and the end of the glass was black.

Concerned about the K2 and the power supply I connected an alternate power
cable and every thing checked out with no signs of a problem.

I searched the reflector and found several similar cases and concluded the
fuse holder was not making a good tight connection with the fuse as pointed
out in other posts.

Rather than replace the holder with another glass type fuse I opted for a
mini-blade fuse thinking it was a more positive connection/solution. I found
a mini-blade holder at Radio Shack ( after not finding them at two auto
supply stores) PN 270-1237 as well as the mini-blade fuses. I bought two and
have installed one in each leg of the power cable.

I suggest Elecraft take a look at an alternate fusing for that KAT100 cable.

-----
r/ John N4NAB
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