[Elecraft] Fw: Sudden erratic power/high current problems with K2

[Don Wilhelm]

Bill,

All will be well as long as you give some liberty to the requested vs. 
actual power output while you have the 1N4148 diodes in there - the 
1N5711s are pretty flat with respect to voltage vs. frequency.

Glad to hear you now have a handle on things again.

73,
Don W3FPR

Bill Carpenter wrote:
> I had some 1N4148 diodes in my junkbox so I installed them and all is 
> good again.  The diodes in the KAT100 are fine so I'll order a few 
> 1N5711s and replace the 1N4148s when they come in.
>
> Thanks again!
> ----- Original Message ----- From: "Don Wilhelm" <w3fpr at embarqmail.com>
> To: "Bill Carpenter" <nz0t at cox.net>
> Cc: "elecraft list" <elecraft at mailman.qth.net>
> Sent: Saturday, December 22, 2007 3:17 PM
> Subject: Re: [Elecraft] Fw: Sudden erratic power/high current problems 
> with K2
>
>
>> Bill,
>>
>> That is classic behavior when the KPA100 wattmeter diodes are zapped. 
>> Since the most common failure cause is a static (lightning) surge 
>> from the antenna, you may want to consider replacing the ones in the 
>> KAT100 at the same time.  The diodes are 1N5711s and in the KPA100 
>> are D16 and D17 (near the SO239 jack), and the diodes in the KAT100 
>> are D1 and D2.
>>
>> As explanation for the behavior, the K2 power control loop senses 
>> power at the output with the wattmeters - if there is zero power out 
>> reported, the controls drive harder - so you have a base K2 trying to 
>> drive as hard as possible and the resulting output power is the 
>> maximum that can be produced on any given band.  In other words, the 
>> wattmeter must be working for the K2 to control the output power - 
>> that is the sensing element.
>>
>> 73,
>> Don W3FPR
>>
>>
>> Bill Carpenter wrote:
>>> After some investigation I found that the braid of the coax for the 
>>> Aux RF had frayed at the KPA100 board to just a couple of strands.  
>>> Hoping this was the problem I repaired it but no change.  This all 
>>> seems to be caused by the K2 power control being all or none with no 
>>> intermediate settings.  In low power as I turn the knob clockwise it 
>>> goes from minimal power to full QRP of about 12 watts suddenly and 
>>> when the high power comes on it jumps to full output.  How do I 
>>> approach this problem?  Is it ALC related?
>>>
>>
>
>
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