(no subject)

[W6ODJ]

Dear Don,

Thank you very much for the tip.  I found the problem.  I had 2 turns  
on the secondary (white) of T4 instead of 3.  Fixing that solved both  
the 80 meter and 30 meter problems.  I guess it doesn't like  
impedance mismatch.  If I set the power knob at 14 watts, I now get  
at least 12 watts out (on the W2 readout; not the same as actual  
output of course) on all bands, all with currents under 2.8 A.  So,  
this case is closed.  On to the next one.

You perform a real service for Elecraft assemblers.  I've noted your  
posts helping other people.  We all owe you a very great debt of  
gratitude for your patience (telling frustrated people to check and  
check again, etc.) and your dedication.  Again, thank you.

73,

Oliver Johns
W6ODJ


On 26 Jan 2008, at 6:13 PM, Don Wilhelm wrote:

> 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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