[Elecraft] KPA 100 Low power on 160M

[Andrew Lenton]

Hi Don,

Thanks for that, Putting aside the K2's low power on 160, which no doubt has
a component error value somewhere, the KPA 100 has been working at 111 Watts
for two years until I disturbed the PA last week to make way for the DSP
board. So something has happened to the KPA100. I only get a high current
warning when the KPA100 is in use. 80 to 10 Metres is fine 11 watts no
warnings! I think something has happened to the high power low pass filter,
any thoughts?

73

Andrew G8UUG

-----Original Message-----
From: Don Wilhelm [mailto:w3fpr at embarqmail.com] 
Sent: 24 October 2008 23:57
To: a at lenton.org
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA 100 Low power on 160M

Andrew,

If you cannot get at least 10 watts out of the base K2 over all the 160 
meter band you have a problem in either the 160/80 meter bandpass filter 
or the 160m low pass filter.  I encourage you to look there first.
You will likely have to compromise the bandpass filter settings between 
160 and 80 meters.  Set the filter inductors midway between the peak at 
3700 kHz and 1850 kHz for your initial trial and make slight adjustments 
from there.  Check the coupling inductor to be certin it is the right 
value - your report indicates that the bandpass filter may be more 
narrow than normal.

That being said, low power combined with high current warnings do 
indicate a problem with the low pass filter for that band - be certain 
the capacitors are the correct value and the number of turns on the 
toroids are correct.

If you had not already discovered, the limited power out of the base K2 
is what is likely causing the reduce power from the KPA100.

73,
Don W3FPR

a at lenton.org wrote:
> HI,
>
> I have just fitted the DSP board and it works fine, on
> putting the K2 back together, I fond that 160M will not go
> above 50 Watts and I get a high current warning, All other
> bands are 111 Watts no problem. I am using Rohde & Schwarz
> power probe and a 40dB attenuator, to the match is close to
> 50 OHMS. I have also used my bird through line and get the
> same results. I suspected the band pass filter in the KPA
> 100, I did find what looked a poor joint on L1, but re
> soldering  has not cured the problem. I do not like
> disturbing the PCB and power transistor mounts so need to
> pinpoint quickly. In QRP mode the K2 works fine. ( 6 Watts
> 1800 to 2.000 with 11 watts at 1900 I have never had 10
> Watts + on this band). I will sweep the low pass filter
> tonight, if I find this in order, I will then connect the
> Watt meter directly to input to the low pass filter and see
> if everything is fine at this point. Has any one had this
> before and can give some pointers it would be appreciated?
> The SWR circuit gives 1:1 into the dummy load so is metering
> correctly. Has anyone know C2A, C2B, C2C, C2C, C2D, or CDE
> to fail or indeed L1 and L2
>
> 73
>   
>



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