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KLPA3A power transistor thermal stress concerns

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Nick - VE3EY

KLPA3A power transistor thermal stress concerns

I have a K3s/10 (12 watt version) which I intend to use in the upcoming cq
ww cw contest. This unit does not have KPA3A power brick and cooling fans
installed.

While doing some trial runs I noticed that the area around the KLPA3A power
transistors is getting fairly hot after prolonged contest use. My guess is
the transistors are working harder when used as finals. The rig needs to
produce between 6 and 12 watts to properly drive the SS amp I intend to
use.

Looking for some opinions:

1. Don't worry about it. I am paranoid. The KLPA3A power transistors can
sustain the rigor of 40+ hours use in the contest. Just make sure they are
properly fastened as directed in the assembly manual.

2. Rig up some passive thermal cooling. Perhaps a heat-sink underneath
the rig to allow heat to dissipate.

3. Mount a 12v cooling fan somewhere to allow for airflow underneath the
radio to take away excess heat.

73

Nick VE3EY
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Don Wilhelm

Re: KLPA3A power transistor thermal stress concerns

Nick,

It all depends on your perception of "fairly hot".

My 'rule of thumb' is that if you can hold your fingers on the surface,
then it is not too hot.

73,
Don W3FPR

On 10/24/2017 7:27 AM, Nick - VE3EY wrote:
> I have a K3s/10 (12 watt version) which I intend to use in the upcoming cq
> ww cw contest. This unit does not have KPA3A power brick and cooling fans
> installed.
>
> While doing some trial runs I noticed that the area around the KLPA3A power
> transistors is getting fairly hot after prolonged contest use. My guess is
> the transistors are working harder when used as finals. The rig needs to
> produce between 6 and 12 watts to properly drive the SS amp I intend to
> use.
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Rose

Re: KLPA3A power transistor thermal stress concerns

In reply to this post by Nick - VE3EY

Nick,

What is the "12 watt" version you're referring to?

73

K0PP

On Oct 24, 2017 5:29 AM, "Nick - VE3EY" <[hidden email]> wrote:

> I have a K3s/10 (12 watt version) which I intend to use in the upcoming cq
> ww cw contest. This unit does not have KPA3A power brick and cooling fans
> installed.
>
> While doing some trial runs I noticed that the area around the KLPA3A power
> transistors is getting fairly hot after prolonged contest use. My guess is
> the transistors are working harder when used as finals. The rig needs to
> produce between 6 and 12 watts to properly drive the SS amp I intend to
> use.
>
> Looking for some opinions:
>
> 1. Don't worry about it. I am paranoid. The KLPA3A power transistors can
> sustain the rigor of 40+ hours use in the contest. Just make sure they are
> properly fastened as directed in the assembly manual.
>
> 2. Rig up some passive thermal cooling. Perhaps a heat-sink underneath
> the rig to allow heat to dissipate.
>
> 3. Mount a 12v cooling fan somewhere to allow for airflow underneath the
> radio to take away excess heat.
>
>
>
> 73
>
> Nick VE3EY
> ______________________________________________________________
> 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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Wes Stewart-2

Re: KLPA3A power transistor thermal stress concerns

The K3/10 will output 12W.

That said, based on IMD measurements I have performed I would NEVER run a K3/10
at 12W out. Frankly, with my K3S with the latest rev KLPA3A to keep 3rd order
IMD below 30 dBc, I would throttle it back even more above 18 MHz.

Wes N7WS

On 10/24/2017 6:27 AM, Rose wrote:
> Nick,
>
> What is the "12 watt" version you're referring to?
>
> 73
>
> K0PP

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Elecraft mailing list

Re: KLPA3A power transistor thermal stress concerns

In reply to this post by Nick - VE3EY

The K3/100 switches to the KPA3A at 12 watts. So is there a 2w range
(10-12w) where the KLPA3A is putting out unacceptable IMD? Is there a way to
make the switch at 10w, or should we just avoid that 2w "danger zone"?

73

Mike KD8RQE

In a message dated 10/24/2017 10:56:38 A.M. Eastern Daylight Time,
[hidden email] writes:

The K3/10 will output 12W.

That said, based on IMD measurements I have performed I would NEVER run a
K3/10
at 12W out. Frankly, with my K3S with the latest rev KLPA3A to keep 3rd
order
IMD below 30 dBc, I would throttle it back even more above 18 MHz.

Wes N7WS

On 10/24/2017 6:27 AM, Rose wrote:
> Nick,
>
> What is the "12 watt" version you're referring to?
>
> 73
>
> K0PP

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Nick - VE3EY

Re: KLPA3A power transistor thermal stress concerns

In reply to this post by Don Wilhelm

Hi Don

Good question. I happen to have a Infrared Thermometer. After bashing
at it for about 20 minutes, the temperature in the vicinity of two
transistors (as measured against the bottom cover) peaked at 50 degrees
Celsius (122 F) but it did not go beyond that. I ran the rig at 10 watts
on 10 meters which is where most of the drive power is needed.

I suppose that should be OK than.

73 and thanks for your feedback,
Nick
VE3EY

On Tue, Oct 24, 2017 at 9:23 AM, Don Wilhelm <[hidden email]> wrote:

> Nick,
>
> It all depends on your perception of "fairly hot".
>
> My 'rule of thumb' is that if you can hold your fingers on the surface,
> then it is not too hot.
>
> 73,
> Don W3FPR
>
>
>
> On 10/24/2017 7:27 AM, Nick - VE3EY wrote:
>
>> I have a K3s/10 (12 watt version) which I intend to use in the upcoming cq
>> ww cw contest. This unit does not have KPA3A power brick and cooling fans
>> installed.
>>
>> While doing some trial runs I noticed that the area around the KLPA3A
>> power
>> transistors is getting fairly hot after prolonged contest use. My guess
>> is
>> the transistors are working harder when used as finals. The rig needs to
>> produce between 6 and 12 watts to properly drive the SS amp I intend to
>> use.
>>
>

Don Wilhelm

Re: KLPA3A power transistor thermal stress concerns

Nick,

Yes, I believe that should be no problem.

73,
Don W3FPR

On 10/24/2017 8:57 PM, Nick - VE3EY wrote:

> Hi Don
>
> Good question. I happen to have a Infrared Thermometer. After
> bashing at it for about 20 minutes, the temperature in the vicinity of
> two transistors (as measured against the bottom cover) peaked at 50
> degrees Celsius (122 F) but it did not go beyond that. I ran the rig
> at 10 watts on 10 meters which is where most of the drive power is
> needed.
>
> I suppose that should be OK than.
>
> 73 and thanks for your feedback,
>

Wes Stewart-2

Re: KLPA3A power transistor thermal stress concerns

In reply to this post by Elecraft mailing list

Personally, I would, and do, avoid that region. The difference in received
strength between 10 and 12W is imperceptible if the HPA isn't installed. If it
is installed, crank the power up to 20 or so and you're out of danger.

Wes N7WS

On 10/24/2017 8:31 AM, Mike via Elecraft wrote:

> The K3/100 switches to the KPA3A at 12 watts. So is there a 2w range
> (10-12w) where the KLPA3A is putting out unacceptable IMD? Is there a way to
> make the switch at 10w, or should we just avoid that 2w "danger zone"?
>
> 73
>
> Mike KD8RQE
>
>
> In a message dated 10/24/2017 10:56:38 A.M. Eastern Daylight Time,
> [hidden email] writes:
>
> The K3/10 will output 12W.
>
> That said, based on IMD measurements I have performed I would NEVER run a
> K3/10
> at 12W out. Frankly, with my K3S with the latest rev KLPA3A to keep 3rd
> order
> IMD below 30 dBc, I would throttle it back even more above 18 MHz.
>
> Wes N7WS
>
>

N2TK

Re: KLPA3A power transistor thermal stress concerns

In reply to this post by Don Wilhelm

50C is not hot for a transistor. Commercial transistors are usually speced to 85C. JANS (space) transistors are speced to 125C and actually baked without bias for 320 hours at 200C. The hFE is measured before and after to check for change.
73
N2TK, Tony

Sent from my iPad

> On Oct 24, 2017, at 8:23 PM, Don Wilhelm <[hidden email]> wrote:
>
> Nick,
>
> Yes, I believe that should be no problem.
>
> 73,
> Don W3FPR
>
>> On 10/24/2017 8:57 PM, Nick - VE3EY wrote:
>> Hi Don
>>
>> Good question. I happen to have a Infrared Thermometer. After bashing at it for about 20 minutes, the temperature in the vicinity of two transistors (as measured against the bottom cover) peaked at 50 degrees Celsius (122 F) but it did not go beyond that. I ran the rig at 10 watts on 10 meters which is where most of the drive power is needed.
>>
>> I suppose that should be OK than.
>>
>> 73 and thanks for your feedback,
>>
>
> ______________________________________________________________
> 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]

Nr4c

Re: KLPA3A power transistor thermal stress concerns

Yes. But I believe that is Junction temperature, not case on heatsink temp. Remember the case bottom is heatsink for those. Make sure screws are tight.

Sent from my iPhone
...nr4c. bill

> On Oct 27, 2017, at 12:19 PM, N2TK, Tony <[hidden email]> wrote:
>
> 50C is not hot for a transistor. Commercial transistors are usually speced to 85C. JANS (space) transistors are speced to 125C and actually baked without bias for 320 hours at 200C. The hFE is measured before and after to check for change.
> 73
> N2TK, Tony
>
> Sent from my iPad
>
>> On Oct 24, 2017, at 8:23 PM, Don Wilhelm <[hidden email]> wrote:
>>
>> Nick,
>>
>> Yes, I believe that should be no problem.
>>
>> 73,
>> Don W3FPR
>>
>>> On 10/24/2017 8:57 PM, Nick - VE3EY wrote:
>>> Hi Don
>>>
>>> Good question. I happen to have a Infrared Thermometer. After bashing at it for about 20 minutes, the temperature in the vicinity of two transistors (as measured against the bottom cover) peaked at 50 degrees Celsius (122 F) but it did not go beyond that. I ran the rig at 10 watts on 10 meters which is where most of the drive power is needed.
>>>
>>> I suppose that should be OK than.
>>>
>>> 73 and thanks for your feedback,
>>>
>>
>> ______________________________________________________________
>> 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]
>
> ______________________________________________________________
> 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]

Don Wilhelm

Re: KLPA3A power transistor thermal stress concerns

Bill is entirely correct.
Once in my prior career, I did a study of Mean Time Between Failure for
IC circuits (same applies to transistors). That study had to consider
the case temperature of the IC (or transistor) with respect to the
junction temperature.
The specification for the IC or transistor package will include a
thermal resistance parameter, which must be considered to obtain the
maximum temperature for the case of the device.

Bill's comment about the screw tightness is entirely correct - the heat
of the device case must be transferred to the heatsink in an efficient
manner.

73,
Don W3FPR

On 10/27/2017 6:07 PM, Nr4c wrote:

> Yes. But I believe that is Junction temperature, not case on heatsink temp. Remember the case bottom is heatsink for those. Make sure screws are tight.
>
> Sent from my iPhone
> ...nr4c. bill
>
>
>> On Oct 27, 2017, at 12:19 PM, N2TK, Tony <[hidden email]> wrote:
>>
>> 50C is not hot for a transistor. Commercial transistors are usually speced to 85C. JANS (space) transistors are speced to 125C and actually baked without bias for 320 hours at 200C. The hFE is measured before and after to check for change.
>>

Clay Autery-2

Re: KLPA3A power transistor thermal stress concerns

If anyone requires someone to assist in REALLY getting "nutty" about
thermal control/dissipation on electronic components, I'd be happy to
oblige from my experience.
I have had some fairly extensive hand-on experience. Once upon a time,
I invented Arctic Silver thermal compound and adhesive. Before, during,
and after that time I spent thousands of hours working on custom thermal
control solutions.

It's.... an addiction.

73,
Clay KY5G

On 10/27/2017 6:00 PM, Don Wilhelm wrote:

> Bill is entirely correct.
> Once in my prior career, I did a study of Mean Time Between Failure
> for IC circuits (same applies to transistors). That study had to
> consider the case temperature of the IC (or transistor) with respect
> to the junction temperature.
> The specification for the IC or transistor package will include a
> thermal resistance parameter, which must be considered to obtain the
> maximum temperature for the case of the device.
>
> Bill's comment about the screw tightness is entirely correct - the
> heat of the device case must be transferred to the heatsink in an
> efficient manner.
>
> 73,
> Don W3FPR
>
> On 10/27/2017 6:07 PM, Nr4c wrote:
>> Yes. But I believe that is Junction temperature, not case on heatsink
>> temp. Remember the case bottom is heatsink for those. Make sure
>> screws are tight.
>>
>> Sent from my iPhone
>> ...nr4c. bill
>>
>>
>>> On Oct 27, 2017, at 12:19 PM, N2TK, Tony <[hidden email]> wrote:
>>>
>>> 50C is not hot for a transistor. Commercial transistors are usually
>>> speced to 85C. JANS (space) transistors are speced to 125C and
>>> actually baked without bias for 320 hours at 200C. The hFE is
>>> measured before and after to check for change.