strange K2 160m power problem

[Torsten Clay]

In the process of calibrating my LP100 wattmeter, I was hopping back and forth
between bands and transmitting. I discovered a strange problem with my K2/100
#3134. This is what happens:

First, I have the K2 hooked up to a dummy load. I also confirmed that this
happens with a different wattmeter in line. I am keying the K2 with a straight
key.

1. I transmit on 28 MHz. I get about 100w out.
     I press "band -" several times until I get to 1.8 MHz. Putting the
     key down, I get about 110 w out as expected.

2. I transmit on 28 MHz. I get about 100w out.
     I press "band +" once to get to 1.8 MHz. Putting the key down, I get
     170 w out !!!

In other words, it makes a difference whether I go from 10m to 160m either by
pressing Band - several times, or Band + once. Pressing Band + once somehow
screws up the tx agc. The problem does not seem to be in the KPA100, because if
I turn the power down to 10W I get similar response (10W one way, 15W the other
way).

My other K2 (similar SN) does not do this, or if there is a difference in the
160m power it is too small to notice. The only thing different about #3134 is
that is has somewhat lower 10m tx power, about 7W max without the KPA100. But
it can still make 100w on 10m with the KPA/100.

Ideas?? If I twiddle the power control AFTER I start transmitting on 160, the
power returns to the correct level from 170w.

I think this caused me to smoke the matching network on my 160m shunt-fed
vertical during the IARU contest. I was driving an Ameritron AL1500 amp, which
only needs about 50w drive to make 1500w out. When I first went to 160 in the
contest, the swr jumped like crazy, and I confirmed by going outside that a
doorknob cap in the shunt feed was smoking! I can't remember if I was on 10m
before I qsyed to 160, but it is possible since I made a bunch of contacts
there. I suspect that the increased drive put me way over 1500w for a short
time.

Torsten
N4OGW/5
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[Torsten Clay]

On Wed, 19 Jul 2006, R. Torsten Clay wrote:

> In the process of calibrating my LP100 wattmeter, I was hopping back and
> forth between bands and transmitting. I discovered a strange problem with my
> K2/100 #3134. This is what happens:
>
> First, I have the K2 hooked up to a dummy load. I also confirmed that this
> happens with a different wattmeter in line. I am keying the K2 with a
> straight key.
>
> 1. I transmit on 28 MHz. I get about 100w out.
>     I press "band -" several times until I get to 1.8 MHz. Putting the
>     key down, I get about 110 w out as expected.
>
> 2. I transmit on 28 MHz. I get about 100w out.
>     I press "band +" once to get to 1.8 MHz. Putting the key down, I get
>     170 w out !!!
>
> In other words, it makes a difference whether I go from 10m to 160m either by
> pressing Band - several times, or Band + once. Pressing Band + once somehow
> screws up the tx agc. The problem does not seem to be in the KPA100, because
> if I turn the power down to 10W I get similar response (10W one way, 15W the
> other way).
>

I still don't know why it was doing this. Re-aligning the whole rig did
not help. However, after increasing R98 to 680 Ohms I no longer get 160W
on 160m.

BTW I also tried to fix the low power on 10M. I rewound T4, T2, adjusted
the output filters, fiddled with T1, and peaked very carefully. In the end
I gained maybe 1 W, now 8W max on 10M (without KPA100).

Torsten
N4OGW

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