Posted by
jperelst on
Sep 27, 2010; 1:53am
URL: http://elecraft.85.s1.nabble.com/K2-Heat-On-Digital-Modes-tp5572168p5573350.html
Don,
Again, thanks for quick reply.
Guess I know what I'll be doing this weekend. That's okay, I was going to open
it up anyway to adjust the SSB filters to get narrow filtering for use in
digital modes.
Jon
KB1QBZ
________________________________
From: Don Wilhelm <
[hidden email]>
To: Jon Perelstein <
[hidden email]>
Cc: elecraft reflector <
[hidden email]>
Sent: Sun, September 26, 2010 7:12:49 PM
Subject: Re: [Elecraft] K2: Heat On Digital Modes
Jon,
Your quick tests are sufficient to negate my initial suspicion.
I would say your next step is to re-do the KPA100 bias adjustment. If you
have the bias set too high, the PA transistors will heat more than normal.
Meter the current into the KPA100 - put the K2 into CW test (hold the VOX
button) and make sure the "C" indicator in the display is blinking - connect
a dummy load to the KPA100 'just in case'. Set power to greater than 11
watts. The current draw will be in the vicinity of 500 ma. Whatever your
external ammeter says, add 400 ma to that - this is your target value.
The hold TUNE, and look at the ammeter - If it is a digital meter, wait
until the 2nd reading (blink) because the first value shown may be too low
due to the relative timing of the meter vs the time you pushed the TUNE
button.
The current will go up the longer you remain in TUNE, so obtain the reading
and exit tune - adjust the KPA100 bias up or down a bit and try again. Once
you have hit your target value, you are done - be sure to remove the ammeter
from the power line.
While you have the shield off the KPA100, you may want to check the balance
on the wattmeter (C1 adjustment) and the power calibration with reference to
a wattmeter that you are willing to trust.
You should be ale to operate the KPA100 at 35 watts continuously without it
getting too hot to touch - yes it will get quite warm, but not too hot to
touch unless you have more sensitive fingers than average. RTTY can be
considered continuous, PSK31 should be OK up to 50 watts since the PSK idle
has a shorter duty cycle.
If the bias and wattmeter are correct, and you still feel it is getting
warmer than you would like, you might want to try a supplemental fan - find
one from a defunct computer, and run it with a resistor in series to slow it
down so the noise does not irritate. It can be placed on top of the heat
sink, moving air away and will be quite effective. See Tom Hammond's
website www.n0ss.net for his implementation.
73,
Don W3FPR
On 9/26/2010 6:49 PM, Jon Perelstein wrote:
Don
>
>
>Thanks for the quick reply. Fortunately, it appears that uncontrolled
>power output is not the problem.
>
>
>And yes, it is a K2/100.
>
>
>I connected the rig to an MFJ-941E Versatuner II and connected the
>Versatuner to my antenna. I tuned to a 1.1:1 SWR using the Versatuner
>and then measured forward power on CW key down at various power
>settings. The forward power transitioned smoothly from just under 20
>watts with the rig set to 20 watts to just over 90 watts with the rig
>set to 100 watts. I probably need to do some calibration, but it
>appears that the power control is working.
>
>
>I also tried it with PSK and Olivia transmissions and the Versatuner
>was showing around 25 watts when I had 25 watts set on the K2's power
>control. I upped the K2s power control to 40 watts and saw an
>increase in forward power on the Versatuner to about 35 watts or so.
>
>
>I can get my hands on a real wattmeter in the next few days if you
>think it necessary, but these tests would imply that I am not
>experiencing uncontrolled power.
>
>
>Jon
>KB1QBZ
>
>
>
>
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