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[K2] KPA100 Temp Cal: Room temp or radio temp?

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[K2] KPA100 Temp Cal: Room temp or radio temp?

Brian - N5BCN
I may be wandering into nit-picky land, but I noticed using a hand held infrared thermometer that the heat sink of the KPA100 is usually about 2 degrees warmer than ambient air temperature (when the unit has been sitting idle for several hours).  For example, the heat sink will measure about 26 degs C and the room air temp is about 24 degs C.

For the purposes of the CAL tPA, which temp should I go with?  Or does it really even matter?

Secondarily, when I discovered all this, I also found out that I had never calibrated CAL tPA!  I was wondering why the fan NEVER seemed to kick on!  So, I've been using the KPA100 for YEARS without the benefit of the fan.  I hope I didn't cause any long term degradation of the unit.

Incidentally, it always seemed to get out at the proper power, but boy would it get hot!

73,
Brian N5BCN
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Re: [K2] KPA100 Temp Cal: Room temp or radio temp?

Don Wilhelm-4
Brian,

If you let the KPA100 cool for a sufficient time, the heatsink should be
at the ambient temperature.  How long is long enough will vary from
temperature to temperature.  I suggest that power off for 30 minutes or
more will give good results.

You need to measure the temperature directly below the PA transistors -
which is difficult to do.  The best solution is to let everything to
acclimate to ambient and set CAL TMP at whatever the ambient temperature
may be (in degC).   How much do you trust your infrared thermometer is
the real question.  2 degrees may not make a big difference.  Light on
the heatsink can create an apparent difference in temperature.  The
heatsink can absorb light and  make it warmer than the ambient temperature.

IMHO, 2 degrees C will not make that much difference in when the fan
comes on to either low or high speed.

In other words, go with whatever is comfortable with you.  The CAL TPA
parameter only defines when the fan will be activated.  Some KPA100
owners who want to see the fan come on sooner than normal will set the
CAL TPA menu parameter to a greater temperature than ambient.  In other
words, setting CAL TPA to 30 degC when the ambient is 23 degC will turn
on the fan earlier than the normal heatsink temperature.

Bottom line -- it is an individual decision (but don't go to extremes).

73,
Don W3FPR

On 2/9/2016 8:22 PM, Brian - N5BCN via Elecraft wrote:

> I may be wandering into nit-picky land, but I noticed using a hand held
> infrared thermometer that the heat sink of the KPA100 is usually about 2
> degrees warmer than ambient air temperature (when the unit has been sitting
> idle for several hours).  For example, the heat sink will measure about 26
> degs C and the room air temp is about 24 degs C.
>
> For the purposes of the CAL tPA, which temp should I go with?  Or does it
> really even matter?
>
> Secondarily, when I discovered all this, I also found out that I had never
> calibrated CAL tPA!  I was wondering why the fan NEVER seemed to kick on!
> So, I've been using the KPA100 for YEARS without the benefit of the fan.  I
> hope I didn't cause any long term degradation of the unit.
>
> Incidentally, it always seemed to get out at the proper power, but boy would
> it get hot!
>
> 73,
> Brian N5BCN
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-KPA100-Temp-Cal-Room-temp-or-radio-temp-tp7613845.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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Re: [K2] KPA100 Temp Cal: Room temp or radio temp?

mjpilgrim
I have a related question: I purchased my K2/100 only a month ago, second hand, SN 5818.  I've experienced "PA HOT" shut down on several occasions when running 100Watts out, and less frequently but it has happened when at 50Watts.  I've witnessed the discussion of setting Cal tPa to ambient temp. C, and with my indoor/outdoor digital weather monitor on my operating desk, I see 81 F as a normal workstation temp, which converts to 26.95 C...... that is the figure I enter into the Cal tPa setting.  I can then operate CW for a few minutes, noticing that the fan does turn on.  Unfortunately, since I do not continually keep my eyes on the digital display as I continue my CW qso, I have been frequently surprised to note that I have experienced a Pa Hot failure and my output has shut down (although the side tone monitor continues to yield my keyed side tone).  

I have now noticed that when that failure occurs, I can power down the K2 and immediately power it pack on, and I then can continue operating with full output power.  This almost appears as if the Pa Hot error is a false indication, and even though it initially shuts down my output power, it seems strange that it resets to normal ops when power is cycled off and on again.  I have failed to notice if the fan comes on upon the power off/on recycle..... I'm thinking it is not on at that time.  I'll try to be more observant on future failures but in the meantime I wanted to mention this failure in case I am overlooking something or maybe doing something to create harm by powering off and on the K2.

PS.  While attempting to change the failing conditions, I have increased the Cal tPa temp up to as high as 33C, and I believe that is where it was set with my most recent failure.

Any ideas out there?  Thanks.
Mike, K5MP
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Re: [K2] KPA100 Temp Cal: Room temp or radio temp?

Don Wilhelm-4
Mike,

First, the menu CAL TPA parameter will indicate the temperature of the
heatsink if all is working normally.  That is why you let the heatsink
cool to ambient temperature before setting CAL TPA.  If you have a
temperature probe that can measure the heatsink temperature at the PA
transistor mounting point, you don't have to let it cool to ambient,
just set it to the actual heatsink temperature - but most hams do not
have accurate temperature measurement equipment, so cooling to ambient
is the normal procedure.
Set CAL TPA first before proceeding with anything else.

Did you purchase this KPA100 as a new kit or did you purchase it used?
It may have a fault or a badly soldered connection that changes when the
temperature rises - but I suspect you may have a power control problem.

Make a check on the power output - connect it to an external wattmeter
and a dummy load.
Set the power level for 50 watts and do a TUNE - the power on your
wattmeter and the K2 display should indicate about 20 watts.
If you see 20 watts on both the K2 display and the external wattmeter,
then proceed and do a TUNE/DISPLAY - in other words, depress both the
TUNE and DISPLAY buttons together.  You should see about 50 watts
indicated on both the external wattmeter and the K2 display.

If either or both those tests fail, I suspect you will see a low power
indicated on the K2 display while seeing a high power (120 watts or
greater) on the external wattmeter.
What that means is you have no power control and the KPA100 is going to
its fully capable output at all times.
The cause of that behavior is damaged diodes in the KPA100 wattmeter -
diodes D16 and D17 located on the board close to the SO-239 jack.

In other words, if your KPA100 is going to full power output all the
time, it will heat rapidly and give you a PA HOT message.  More common
is a HiCURR message, but if you have the CAL CUR set above 3.50 amps,
you may not get that warning.

If the power control is working normally, then you should look into the
PA Bias and the temperature sensing transistor Q3 or its input to the
Firmware IC U1.

Yes, it is OK to turn power off or even to pull the power plug, that in
itself will not cause a problem with the K2 - the K3 and KX3 are
different in that respect, and they should be powered off normally.

73,
Don W3FPR


On 3/27/2016 5:24 PM, mjpilgrim wrote:

> I have a related question: I purchased my K2/100 only a month ago, second
> hand, SN 5818.  I've experienced "PA HOT" shut down on several occasions
> when running 100Watts out, and less frequently but it has happened when at
> 50Watts.  I've witnessed the discussion of setting Cal tPa to ambient temp.
> C, and with my indoor/outdoor digital weather monitor on my operating desk,
> I see 81 F as a normal workstation temp, which converts to 26.95 C......
> that is the figure I enter into the Cal tPa setting.  I can then operate CW
> for a few minutes, noticing that the fan does turn on.  Unfortunately, since
> I do not continually keep my eyes on the digital display as I continue my CW
> qso, I have been frequently surprised to note that I have experienced a Pa
> Hot failure and my output has shut down (although the side tone monitor
> continues to yield my keyed side tone).
>
> I have now noticed that when that failure occurs, I can power down the K2
> and immediately power it pack on, and I then can continue operating with
> full output power.  This almost appears as if the Pa Hot error is a false
> indication, and even though it initially shuts down my output power, it
> seems strange that it resets to normal ops when power is cycled off and on
> again.  I have failed to notice if the fan comes on upon the power off/on
> recycle..... I'm thinking it is not on at that time.  I'll try to be more
> observant on future failures but in the meantime I wanted to mention this
> failure in case I am overlooking something or maybe doing something to
> create harm by powering off and on the K2.
>
> PS.  While attempting to change the failing conditions, I have increased the
> Cal tPa temp up to as high as 33C, and I believe that is where it was set
> with my most recent failure.
>
> Any ideas out there?  Thanks.
> Mike, K5MP
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-KPA100-Temp-Cal-Room-temp-or-radio-temp-tp7613845p7615600.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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Re: [K2] KPA100 Temp Cal: Room temp or radio temp?

John / 9V1VV
This post has NOT been accepted by the mailing list yet.
This is a year late but it may help myone with heat problems...

After ten years of using the K2 in the tropics, usually in  non-airconditioned room, I came to the conclusion that the cooling arrangment used is not efficient.

You have a tiny fan blowing air from outside onto the two PA transistors and associated components, but the heat has nowhere to go. The enclosure is sealed so all that happens is the K2 gets filled with hot air from the transistors.

To improve the situation drastically I removed the internal speaker (I use an external one) and replaced it with a 12V/0.17A axial fan which has the same mounting hole spacing. Cost me $2.

To drive the fan I used a PNP TO3 transistor (almost any will do) as an emitter-follower. Connect as follows:

Base to fan- on the main  pcb
Emitter to black fan lead
Collector to ground
Red fan lead to +12VCTRL line

It is not a good idea to drive the fan in parallel with the existing small one because the Darlington pair IC driver may be overloaded.


Now the hot air is ejected. The result is that the K2 heatsink runs cooler and the high fans don't cut in so often. Duty cycle is improved on CW - you can key down at 100 Watts for 2 minutes no problem. At a 50% duty cycle at 100 W (maximum use on CW) you can go all day.

73

John 9V1VV
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