Jerry,
It sounds like some RF from the KPA100 could be getting into the base K2.
Is your KPA100 upgraded with the latest updates, AND the new shield?
For the latest update, peek between the shield and the board - If you
see blue toroid cores at RFC1 and L16, then it is up to date - OTOH, if
you see red core toroids at L15 and L16, install KPA100UPKT.
On the shield, it should have spring clips to ground it to the sides of
the base K2 - make certain that the area where the spring clips contact
the sides of the base K2 has been cleared of all paint - sandpaper works.
Also check the width of the slot in the shield next to the SO239 ANT
jack - it should be only a bit wider than 1/8 inch. If it is the older
wide slot, replace the shield with KPA100SHLDKT.
Also, there should be 2 bent-over solder lugs that connect the top of
the shield to the SO239 jack. Make sure they are soldered together. If
missing, they are supplied as part of KPA100SHLDKT.
73,
Don W3FPR
On 9/4/2021 5:03 PM, jerry wrote:
Hi Elecraft list & Bob,
Sigh. Sometimes it don't pay to get up in the morning.
First, I was having a CW QSO on 40M with a station in the East Coast...
My K2/10 was driving the Tiny Linear - we were seeing 150W on the meter.
Suddenly, the screen of the linear flashed bright white, and the RF
went away, leaving me with the barefoot K2.
Seems that 150W was Just Too Much for the little fan-driven heat
sink, and the PA transistor shorted out. My fault, of course. I have
a few more of those transistors, but I'll have to hold the power down,
instrument the heat sink temperature, and put in some sort of protection.
In the meantime...
I installed the recently acquired KPA100 in my K2. Actually, that
KPA100 came from ANOTHER K2, acquired on Ebay. I swapped it into my
first K2, because that one has the V2 mods, including the upgraded
crystals.
So here I am, ready to continue hamming. My K2 ( now /100 ) is
doing strange rf-in-the-shack'y things. If I send a bit of CW, my
sent CW starts breaking up, and strange pops and clicks (like relays )
come out of the radio. Then when I stop sending, the radio is
completely silent - no audio. I can see band noise and signals on the
S-meter(bargraph) but no audio WHATSOEVER. Hitting a band button or
the display button fixes it, and audio is back.
Sometimes OTOH, when I stop transmitting, the audio comes back much
LOUDER than it was before I transmitted.
This all happens at any power level where the final is engaged. If I
turn the power down to 8W or so, all is good. If otoh, I turn the
power knob anywhere past that *click* where the PA comes on line, the
bad things happen. Even at, say, 12W.
I made up a short length of RG8/U with 4 Palomar 31-mix giant
ferrite beads - a common mode choke. No difference.
With a dummy load, all is good. No fuss no muss, it just transmits
nice.
The antenna is very low SWR. It is a 6BTV vertical about 100 feet
up the hill from the house. There is an MFJ998RT remote autotuner up
at the base of the antenna. It is grounded with an Ufer ground - 80
feet of #6 copper wire
buried in the concrete pad, which is 70 feet long by 10 feet wide.
If I turn the PA off, the K2 behaves well, even at the full 15W.
Tune mode shows SWR 1.2 to 1. My K2 btw has the KDSP2 audio filter.
- Jerry KF6VB
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