[K2] Hi Cur questions

[W6ODJ]

Dear folks,

I'm wondering if this is a bug, or perhaps a known feature of the  
K2.  Comments appreciated.

The following observations are made with the Max current set to 3.5  
A.  The K2 is running into a DL1 dummy load, directly connected by a  
male-male BNC adapter.  The KAT2 is not installed.  The power supply  
is rated at 4 A continuous, 6 A intermittent.  There is very little  
drop in the nominal 13.6 voltage when the Xmtr is keyed.  The BP  
filters have been aligned carefully as per the manual page 80.

On 40, 20, 17, 15, 12, 10 meters, I can set the Power knob on the K2  
to its maximum of 15.2 Watts with no sign of Hi Cur.  The actual  
current drains run somewhere around 2.5 A.  The actual power out  
varies, of course, but there is no problem with Hi Cur.  The powers  
read from the display are:  40 = 14.9   20 = 14.5   17 = 14.6   15 =  
14.1   12 = 10.9   10 = 10.0.  Notice that the power decreases on 12  
and 10, as evidently would be expected since the final is less  
efficient on these high bands.

But on 80 meters, there will be Hi Cur for any power knob setting  
above 8 Watts.  At 8 Watts, the power read from the display is 8.1  
Watts and the current drain is about 2.25 A.  But much above that and  
the current goes to the maximum and is then limited back.

And on 30 meters there will be Hi Cur for any power knob setting  
above 10 Watts.  At 10 Watts, the power read from the display is 9.8  
Watts and the current drain is 3.4 A.

The 30 meter case is particularly puzzling to me.  The BP inductors  
for 30 meters are shared with 20 meters, and the LP filter for the  
two bands is the same.  So any soldering error there would probably  
also show up on 20 meters.  And 30 meters is lower in frequency than  
20 meters and so should be more not less efficient.

I have examined, re-soldered, etc., everything in the BP and LP  
filters for 80 meters.

Any ideas, or is this just normal behavior?

Tnx,

Oliver Johns
W6ODJ
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[Don Wilhelm-4]

Oliver,

High Current coupled with low power output is normally an indication of
a problem with the Low Pass Filter or with T4.  The first thing to check
is the Low Pass Filter.  Check the capacitor values for the 20/30 meter
(and 80 meter) low pass and count (and recount) the turns on the
toroids.  Be certain to count only the turns that pass through the
center of the core.

Check to be certain T4 is wound correctly - 2 turns of green wire and 3
turns of white wire.

As a last resort, there may be a problem with one of the PA output
transistors (Q7 and Q8).  One could be weak and hogging current in an
attempt to produce the requested power output - they have sufficient
gain on some bands to produce adequate power even if one is weak.  The
easiest way to determine that is to replace them both.

73,
Don W3FPR
Oliver Johns wrote:

> Dear folks,
>
> I'm wondering if this is a bug, or perhaps a known feature of the K2.  
> Comments appreciated.
>
> The following observations are made with the Max current set to 3.5
> A.  The K2 is running into a DL1 dummy load, directly connected by a
> male-male BNC adapter.  The KAT2 is not installed.  The power supply
> is rated at 4 A continuous, 6 A intermittent.  There is very little
> drop in the nominal 13.6 voltage when the Xmtr is keyed.  The BP
> filters have been aligned carefully as per the manual page 80.
>
> On 40, 20, 17, 15, 12, 10 meters, I can set the Power knob on the K2
> to its maximum of 15.2 Watts with no sign of Hi Cur.  The actual
> current drains run somewhere around 2.5 A.  The actual power out
> varies, of course, but there is no problem with Hi Cur.  The powers
> read from the display are:  40 = 14.9   20 = 14.5   17 = 14.6   15 =
> 14.1   12 = 10.9   10 = 10.0.  Notice that the power decreases on 12
> and 10, as evidently would be expected since the final is less
> efficient on these high bands.
>
> But on 80 meters, there will be Hi Cur for any power knob setting
> above 8 Watts.  At 8 Watts, the power read from the display is 8.1
> Watts and the current drain is about 2.25 A.  But much above that and
> the current goes to the maximum and is then limited back.
>
> And on 30 meters there will be Hi Cur for any power knob setting above
> 10 Watts.  At 10 Watts, the power read from the display is 9.8 Watts
> and the current drain is 3.4 A.
>
> The 30 meter case is particularly puzzling to me.  The BP inductors
> for 30 meters are shared with 20 meters, and the LP filter for the two
> bands is the same.  So any soldering error there would probably also
> show up on 20 meters.  And 30 meters is lower in frequency than 20
> meters and so should be more not less efficient.
>
>

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