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KPA500 Questions about power and efficiency

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Richard Stutsman

KPA500 Questions about power and efficiency

I've had my KPA500 for a couple of weeks, now, and I have questions
relating to its efficiency as a function of power output and band. A friend
of mine recommended that I run only 300 watts output most of the time in
order to preserve the life of the FETs. I told him that I didn't spend
$2300 on an amp just to get less than 5 dB of gain in my signal (over my
100-watt exciter) instead of the 7 or 8 dB I paid for. Am I wrong?

I took a lot of data this morning that indicates that there is an inverse
relationship between output power and efficiency - to the extent that, down
to about 300 watts, I find that the amount of heat the finals have to
dissipate is less, the higher the power output. This is rather
anti-intuitive.

And if that is true, then wouldn't it be better for the finals if I
routinely ran the amp at the higher power, so long as voltage, current, and
temperature remain within safe limits? Is it safe to run 600 watts on CW,
especially on 80 and 160 meters, where the efficiency appears to be so good
that the finals run cool at 600 watts - even cooler than at 500 watts?

The following data was taken while transmitting into a dummy load. I
adjusted the drive power to obtain one of several predefined output power
levels and then measured input volts and amps and calculated input power
(HV x Current), power dissipation (Input - Output), and efficiency
(Input/Output). Each measurement was taken after about one second of key
down in CW mode. Doing the calculations in between each test allowed the
finals and dummy load to cool off. I never heard the fan come on. Drive,
Output, Input and Dissipation are in Watts. I have shown voltages falling
slightly below 60.0 in red, but I had no problem getting 600 watts output
with less than 40 watts of drive, even in those cases.

*Band Drive Output Volts Amps Input Dissipation Efficiency*

1.8 23 500 64.3 10.2 654 154 76%
30 600 63.9 10.9 697 97 86%

3.5 23 500 65.1 9.4 612 112 82%
30 600 63.2 10.5 664 64 90%

5 24 500 63.7 11.2 707 207 71%
30 600 62.8 12.0 754 154 80%

7 27 500 62.3 12.5 779 279 64%
35 600 61.2 13.8 845 245 71%

10 32 500 61.2 13.4 820 320 61%
39 600 59.8 14.6 873 273 69%

14 15 225 63.4 9.6 609 384 37%
20 310 62.9 11.5 723 413 43%
24 400 61.5 12.8 787 387 51%
33 500 59.0 14.3 844 344 59%
40 600 58.7 15.8 927 327 65%

18 26 490 60.6 12.9 782 392 63%
33 600 59.6 13.8 822 222 73%

21 26 500 60.0 13.9 834 334 60%
35 600 59.8 15.2 909 309 66%

24 23 500 61.4 12.4 761 261 66%
30 600 61.0 13.5 824 224 73%

28 22 500 61.4 12.7 780 280 64%
27 600 60.6 13.8 836 236 72%

Note that in every case there is lower power dissipation (and therefore
less heat generated), the higher the power. I decided to test several lower
power outputs on 20 meters, and I got the maximum dissipation at 310 watts,
and the dissipation at 225 watts was nearly the same as it was at 400 watts.

I should point out that my HV during standby or idle hovered between 79.5
and 80.0 volts. I am using the Red tap wire on the 115-volt input.

And, yes, I know not to use the amp on 60 or 30 meters.

If anybody is going to yell at me for testing a 500-watt amp at 600 watts –
and for proposing to use that much power routinely on 80 meter CW – let me
know your reasoning and why or how you think that would stress the amp.

Oh, and does anybody know if Elecraft would have adjusted the Power
calibration (per band) of the KPA500 kit version, as mentioned in the User
Manau? I found all the settings to be at their default 100%, FWIW. When
comparing at 100 watts to a cheap external watt meter (which agreed with my
TS-590sg power output setting), I found I had to increase power on almost
every band to 104 watts to trip the 100-watt indication on the KPA500's
wattmeters. I decided to leave the settings at their default.

Rick N6IET
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David Olean

Re: KPA500 Questions about power and efficiency

Richard,

The FET amplifier is adjusted for a given power output. You have no
PI Net adjustments with the FET amplifier. It is tweaked to have maximum
efficiency at somewhere near the full rated output. It is all up to the
designer. What you will see is an increase in efficiency as you slowly
turn up the drive level. At somewhere near full power, you will get the
best efficiency. This is normal. The best advice is to not overdrive
the amplifier. Also, keep track of heatsink temperature if you will be
running something like RTTY etc. Excessive heat is bad. I think
running at 600 watts peak is OK as long as you are not dealing with dead
carriers as a rule.

Dave K1WHS

On 1/16/2018 11:14 PM, Richard Stutsman wrote:

> I've had my KPA500 for a couple of weeks, now, and I have questions
> relating to its efficiency as a function of power output and band. A friend
> of mine recommended that I run only 300 watts output most of the time in
> order to preserve the life of the FETs. I told him that I didn't spend
> $2300 on an amp just to get less than 5 dB of gain in my signal (over my
> 100-watt exciter) instead of the 7 or 8 dB I paid for. Am I wrong?
>
> I took a lot of data this morning that indicates that there is an inverse
> relationship between output power and efficiency - to the extent that, down
> to about 300 watts, I find that the amount of heat the finals have to
> dissipate is less, the higher the power output. This is rather
> anti-intuitive.
>
> And if that is true, then wouldn't it be better for the finals if I
> routinely ran the amp at the higher power, so long as voltage, current, and
> temperature remain within safe limits? Is it safe to run 600 watts on CW,
> especially on 80 and 160 meters, where the efficiency appears to be so good
> that the finals run cool at 600 watts - even cooler than at 500 watts?
>
> The following data was taken while transmitting into a dummy load. I
> adjusted the drive power to obtain one of several predefined output power
> levels and then measured input volts and amps and calculated input power
> (HV x Current), power dissipation (Input - Output), and efficiency
> (Input/Output). Each measurement was taken after about one second of key
> down in CW mode. Doing the calculations in between each test allowed the
> finals and dummy load to cool off. I never heard the fan come on. Drive,
> Output, Input and Dissipation are in Watts. I have shown voltages falling
> slightly below 60.0 in red, but I had no problem getting 600 watts output
> with less than 40 watts of drive, even in those cases.
>
> *Band Drive Output Volts Amps Input Dissipation Efficiency*
>
> 1.8 23 500 64.3 10.2 654 154 76%
> 30 600 63.9 10.9 697 97 86%
>
> 3.5 23 500 65.1 9.4 612 112 82%
> 30 600 63.2 10.5 664 64 90%
>
> 5 24 500 63.7 11.2 707 207 71%
> 30 600 62.8 12.0 754 154 80%
>
> 7 27 500 62.3 12.5 779 279 64%
> 35 600 61.2 13.8 845 245 71%
>
> 10 32 500 61.2 13.4 820 320 61%
> 39 600 59.8 14.6 873 273 69%
>
> 14 15 225 63.4 9.6 609 384 37%
> 20 310 62.9 11.5 723 413 43%
> 24 400 61.5 12.8 787 387 51%
> 33 500 59.0 14.3 844 344 59%
> 40 600 58.7 15.8 927 327 65%
>
> 18 26 490 60.6 12.9 782 392 63%
> 33 600 59.6 13.8 822 222 73%
>
> 21 26 500 60.0 13.9 834 334 60%
> 35 600 59.8 15.2 909 309 66%
>
> 24 23 500 61.4 12.4 761 261 66%
> 30 600 61.0 13.5 824 224 73%
>
> 28 22 500 61.4 12.7 780 280 64%
> 27 600 60.6 13.8 836 236 72%
>
> Note that in every case there is lower power dissipation (and therefore
> less heat generated), the higher the power. I decided to test several lower
> power outputs on 20 meters, and I got the maximum dissipation at 310 watts,
> and the dissipation at 225 watts was nearly the same as it was at 400 watts.
>
> I should point out that my HV during standby or idle hovered between 79.5
> and 80.0 volts. I am using the Red tap wire on the 115-volt input.
>
> And, yes, I know not to use the amp on 60 or 30 meters.
>
> If anybody is going to yell at me for testing a 500-watt amp at 600 watts –
> and for proposing to use that much power routinely on 80 meter CW – let me
> know your reasoning and why or how you think that would stress the amp.
>
> Oh, and does anybody know if Elecraft would have adjusted the Power
> calibration (per band) of the KPA500 kit version, as mentioned in the User
> Manau? I found all the settings to be at their default 100%, FWIW. When
> comparing at 100 watts to a cheap external watt meter (which agreed with my
> TS-590sg power output setting), I found I had to increase power on almost
> every band to 104 watts to trip the 100-watt indication on the KPA500's
> wattmeters. I decided to leave the settings at their default.
>
> Rick N6IET
> ______________________________________________________________
> 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]

k6dgw

Re: KPA500 Questions about power and efficiency

In reply to this post by Richard Stutsman

Your KPA500 is designed to produce 500 W at the antenna connector and is
most efficient there. You can watch the PA temp [or put the fans in
automatic and listen to them do it for you]. Field testers were
encouraged to run it at full scale, and they did.

The amplifier was designed for max efficiency at max output. You seem
to have proved the Elecraft designer was successful.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 1/16/2018 3:14 PM, Richard Stutsman wrote:

Don Wilhelm

Re: KPA500 Questions about power and efficiency

In reply to this post by Richard Stutsman

Rick,

I think you are trying to "outwit" the designers.
One thing I can say is that the KPA500 is quite robust and
conservatively rated. One or more of the Field Testers was asked to run
an RTTY contest at "full out" power, and I know one who ran the whole
weekend contest at 700 watts and no problems were detected.

Typical of Elecraft's conservative designs, there are 2 devices, but the
ratings for each device is equal to the stated power output for the
amplifier. Other manufacturers may specify the power for the maximum
ratings for the devices, but not Elecraft.

The FETs in the KPA500 are *each* rated for greater than 500 watts -
that is a total of 1000 watts, so they are "loafing along" at 500 watts.
Similarly with the KPA1500 which uses 2 devices each rated at 1500
watts (3000 watt rating total), the KPA1500 will do legal limit with the
devices loafing along.

Bottom line, the Elecraft amplifiers will do maximum power at a 50% duty
cycle all day long. You should reduce the power for long winded AM
transmissions, but otherwise you can run maximum power.

As far as the efficiency, that is a design compromise. Maximum
efficiency is achieved at somewhere near the maximum rated output. At
levels less than the rated power (or greater than), you can expect the
efficiency to decrease.

Even below the rated power, the devices are running well below their
rated levels, so you are not stressing the FETs by running below 500 watts.

In other words, the designer will set the parameters for the maximum
power rating, and above and below that point, the efficiency will be
lower because the optimal impedance will not be present.

73,
Don W3FPR

On 1/16/2018 6:14 PM, Richard Stutsman wrote:

Jack Brindle-2

Re: KPA500 Questions about power and efficiency

In reply to this post by Richard Stutsman

Hey Richard;

I’m glad you are enjoying our creation. The KPA500 is truly a fine piece of hardware and firmware
that continues to evolve. The most recent firmware version is V1.54, releasing in mid December.

Others have answered many of your questions, let me give my shot at a few. I usually run my
KPA500 in contests at 600 watts. Briefly lighting the 700 watt LED is not unusual, but I don’t
consistently leave it lit. The amplifier is quite comfortable at 600 watts for long periods of time.
Mine is one of the first units and was hand-built, so I can’t claim to have the original PA Deck
installed (it is still sitting on my work bench however), but my current PA Deck is one of the
original shipping versions. After about 10 years, it is working just fine for me.

As for calibration, we perform the cal at the factory for factory-built units, but not for kits.
The reason is that we need to marry the front panel board with the PA Deck to perform these
adjustments, something that is not done until well into assembly. The adjustment values are
kept in memory on the front panel board’s processor. This also means that if you swap the
PA Deck you will need to recalibrate the measurements. Feel free to perform your own
calibration to a known standard. You will probably find that you will need to vary the values
by some small amount to get really accurate measurements. In general they are pretty close
to start off with, but won’t be “right on.”

Enjoy the amplifier, and by all means use it at the power you want. If you have any questions
or need any help, we are here, just ask. You will find customer support to be very helpful.

73!

Jack, W6FB
Elecraft Engineering

> On Jan 16, 2018, at 3:14 PM, Richard Stutsman <[hidden email]> wrote:
>
> I've had my KPA500 for a couple of weeks, now, and I have questions
> relating to its efficiency as a function of power output and band. A friend
> of mine recommended that I run only 300 watts output most of the time in
> order to preserve the life of the FETs. I told him that I didn't spend
> $2300 on an amp just to get less than 5 dB of gain in my signal (over my
> 100-watt exciter) instead of the 7 or 8 dB I paid for. Am I wrong?
>
> I took a lot of data this morning that indicates that there is an inverse
> relationship between output power and efficiency - to the extent that, down
> to about 300 watts, I find that the amount of heat the finals have to
> dissipate is less, the higher the power output. This is rather
> anti-intuitive.
>
> And if that is true, then wouldn't it be better for the finals if I
> routinely ran the amp at the higher power, so long as voltage, current, and
> temperature remain within safe limits? Is it safe to run 600 watts on CW,
> especially on 80 and 160 meters, where the efficiency appears to be so good
> that the finals run cool at 600 watts - even cooler than at 500 watts?
>
> The following data was taken while transmitting into a dummy load. I
> adjusted the drive power to obtain one of several predefined output power
> levels and then measured input volts and amps and calculated input power
> (HV x Current), power dissipation (Input - Output), and efficiency
> (Input/Output). Each measurement was taken after about one second of key
> down in CW mode. Doing the calculations in between each test allowed the
> finals and dummy load to cool off. I never heard the fan come on. Drive,
> Output, Input and Dissipation are in Watts. I have shown voltages falling
> slightly below 60.0 in red, but I had no problem getting 600 watts output
> with less than 40 watts of drive, even in those cases.
>
> *Band Drive Output Volts Amps Input Dissipation Efficiency*
>
> 1.8 23 500 64.3 10.2 654 154 76%
> 30 600 63.9 10.9 697 97 86%
>
> 3.5 23 500 65.1 9.4 612 112 82%
> 30 600 63.2 10.5 664 64 90%
>
> 5 24 500 63.7 11.2 707 207 71%
> 30 600 62.8 12.0 754 154 80%
>
> 7 27 500 62.3 12.5 779 279 64%
> 35 600 61.2 13.8 845 245 71%
>
> 10 32 500 61.2 13.4 820 320 61%
> 39 600 59.8 14.6 873 273 69%
>
> 14 15 225 63.4 9.6 609 384 37%
> 20 310 62.9 11.5 723 413 43%
> 24 400 61.5 12.8 787 387 51%
> 33 500 59.0 14.3 844 344 59%
> 40 600 58.7 15.8 927 327 65%
>
> 18 26 490 60.6 12.9 782 392 63%
> 33 600 59.6 13.8 822 222 73%
>
> 21 26 500 60.0 13.9 834 334 60%
> 35 600 59.8 15.2 909 309 66%
>
> 24 23 500 61.4 12.4 761 261 66%
> 30 600 61.0 13.5 824 224 73%
>
> 28 22 500 61.4 12.7 780 280 64%
> 27 600 60.6 13.8 836 236 72%
>
> Note that in every case there is lower power dissipation (and therefore
> less heat generated), the higher the power. I decided to test several lower
> power outputs on 20 meters, and I got the maximum dissipation at 310 watts,
> and the dissipation at 225 watts was nearly the same as it was at 400 watts.
>
> I should point out that my HV during standby or idle hovered between 79.5
> and 80.0 volts. I am using the Red tap wire on the 115-volt input.
>
> And, yes, I know not to use the amp on 60 or 30 meters.
>
> If anybody is going to yell at me for testing a 500-watt amp at 600 watts –
> and for proposing to use that much power routinely on 80 meter CW – let me
> know your reasoning and why or how you think that would stress the amp.
>
> Oh, and does anybody know if Elecraft would have adjusted the Power
> calibration (per band) of the KPA500 kit version, as mentioned in the User
> Manau? I found all the settings to be at their default 100%, FWIW. When
> comparing at 100 watts to a cheap external watt meter (which agreed with my
> TS-590sg power output setting), I found I had to increase power on almost
> every band to 104 watts to trip the 100-watt indication on the KPA500's
> wattmeters. I decided to leave the settings at their default.
>
> Rick N6IET
> ______________________________________________________________
> 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]

KQ5S-Tom

Re: KPA500 Questions about power and efficiency

I did it again. I meant to send this to the group but sent it to Jack
direct. Sorry Jack.

"The most recent firmware version is V1.54, releasing in mid December."

I went to the software page and it says the most recent beta release is MCU
1.52 Nov 17, 2017 and production release is 1.47.

-----------------
73,
Tom - KQ5S

On Tue, Jan 16, 2018 at 7:18 PM, Jack Brindle <[hidden email]> wrote:

> Hey Richard;
>
> I’m glad you are enjoying our creation. The KPA500 is truly a fine piece
> of hardware and firmware
> that continues to evolve. The most recent firmware version is V1.54,
> releasing in mid December.
>
> Others have answered many of your questions, let me give my shot at a few.
> I usually run my
> KPA500 in contests at 600 watts. Briefly lighting the 700 watt LED is not
> unusual, but I don’t
> consistently leave it lit. The amplifier is quite comfortable at 600 watts
> for long periods of time.
> Mine is one of the first units and was hand-built, so I can’t claim to
> have the original PA Deck
> installed (it is still sitting on my work bench however), but my current
> PA Deck is one of the
> original shipping versions. After about 10 years, it is working just fine
> for me.
>
> As for calibration, we perform the cal at the factory for factory-built
> units, but not for kits.
> The reason is that we need to marry the front panel board with the PA Deck
> to perform these
> adjustments, something that is not done until well into assembly. The
> adjustment values are
> kept in memory on the front panel board’s processor. This also means that
> if you swap the
> PA Deck you will need to recalibrate the measurements. Feel free to
> perform your own
> calibration to a known standard. You will probably find that you will need
> to vary the values
> by some small amount to get really accurate measurements. In general they
> are pretty close
> to start off with, but won’t be “right on.”
>
> Enjoy the amplifier, and by all means use it at the power you want. If you
> have any questions
> or need any help, we are here, just ask. You will find customer support to
> be very helpful.
>
> 73!
>
> Jack, W6FB
> Elecraft Engineering
>
>
> > On Jan 16, 2018, at 3:14 PM, Richard Stutsman <[hidden email]> wrote:
> >
> > I've had my KPA500 for a couple of weeks, now, and I have questions
> > relating to its efficiency as a function of power output and band. A
> friend
> > of mine recommended that I run only 300 watts output most of the time in
> > order to preserve the life of the FETs. I told him that I didn't spend
> > $2300 on an amp just to get less than 5 dB of gain in my signal (over my
> > 100-watt exciter) instead of the 7 or 8 dB I paid for. Am I wrong?
> >
> > I took a lot of data this morning that indicates that there is an inverse
> > relationship between output power and efficiency - to the extent that,
> down
> > to about 300 watts, I find that the amount of heat the finals have to
> > dissipate is less, the higher the power output. This is rather
> > anti-intuitive.
> >
> > And if that is true, then wouldn't it be better for the finals if I
> > routinely ran the amp at the higher power, so long as voltage, current,
> and
> > temperature remain within safe limits? Is it safe to run 600 watts on CW,
> > especially on 80 and 160 meters, where the efficiency appears to be so
> good
> > that the finals run cool at 600 watts - even cooler than at 500 watts?
> >
> > The following data was taken while transmitting into a dummy load. I
> > adjusted the drive power to obtain one of several predefined output power
> > levels and then measured input volts and amps and calculated input power
> > (HV x Current), power dissipation (Input - Output), and efficiency
> > (Input/Output). Each measurement was taken after about one second of key
> > down in CW mode. Doing the calculations in between each test allowed the
> > finals and dummy load to cool off. I never heard the fan come on. Drive,
> > Output, Input and Dissipation are in Watts. I have shown voltages falling
> > slightly below 60.0 in red, but I had no problem getting 600 watts output
> > with less than 40 watts of drive, even in those cases.
> >
> > *Band Drive Output Volts Amps Input Dissipation Efficiency*
> >
> > 1.8 23 500 64.3 10.2 654 154 76%
> > 30 600 63.9 10.9 697 97 86%
> >
> > 3.5 23 500 65.1 9.4 612 112 82%
> > 30 600 63.2 10.5 664 64 90%
> >
> > 5 24 500 63.7 11.2 707 207 71%
> > 30 600 62.8 12.0 754 154 80%
> >
> > 7 27 500 62.3 12.5 779 279 64%
> > 35 600 61.2 13.8 845 245 71%
> >
> > 10 32 500 61.2 13.4 820 320 61%
> > 39 600 59.8 14.6 873 273 69%
> >
> > 14 15 225 63.4 9.6 609 384 37%
> > 20 310 62.9 11.5 723 413 43%
> > 24 400 61.5 12.8 787 387 51%
> > 33 500 59.0 14.3 844 344 59%
> > 40 600 58.7 15.8 927 327 65%
> >
> > 18 26 490 60.6 12.9 782 392 63%
> > 33 600 59.6 13.8 822 222 73%
> >
> > 21 26 500 60.0 13.9 834 334 60%
> > 35 600 59.8 15.2 909 309 66%
> >
> > 24 23 500 61.4 12.4 761 261 66%
> > 30 600 61.0 13.5 824 224 73%
> >
> > 28 22 500 61.4 12.7 780 280 64%
> > 27 600 60.6 13.8 836 236 72%
> >
> > Note that in every case there is lower power dissipation (and therefore
> > less heat generated), the higher the power. I decided to test several
> lower
> > power outputs on 20 meters, and I got the maximum dissipation at 310
> watts,
> > and the dissipation at 225 watts was nearly the same as it was at 400
> watts.
> >
> > I should point out that my HV during standby or idle hovered between 79.5
> > and 80.0 volts. I am using the Red tap wire on the 115-volt input.
> >
> > And, yes, I know not to use the amp on 60 or 30 meters.
> >
> > If anybody is going to yell at me for testing a 500-watt amp at 600
> watts –
> > and for proposing to use that much power routinely on 80 meter CW – let
> me
> > know your reasoning and why or how you think that would stress the amp.
> >
> > Oh, and does anybody know if Elecraft would have adjusted the Power
> > calibration (per band) of the KPA500 kit version, as mentioned in the
> User
> > Manau? I found all the settings to be at their default 100%, FWIW. When
> > comparing at 100 watts to a cheap external watt meter (which agreed with
> my
> > TS-590sg power output setting), I found I had to increase power on almost
> > every band to 104 watts to trip the 100-watt indication on the KPA500's
> > wattmeters. I decided to leave the settings at their default.
> >
> > Rick N6IET
> > ______________________________________________________________
> > 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]

Bob Stevens-3

Re: KPA500 Questions about power and efficiency

In reply to this post by Jack Brindle-2

Well shoot, I'v been using mine at 300 watts to save the finals, no more. I've been driving it with 18 watts out of the K3. What drive power do you recommend? I use it on both CW & SSB. Don't run digital and use my Collins 32V1 and 75A4 on AM.

Sent from my iPad

On Jan 16, 2018, at 7:18 PM, Jack Brindle <[hidden email]> wrote:

Hey Richard;

I’m glad you are enjoying our creation. The KPA500 is truly a fine piece of hardware and firmware
that continues to evolve. The most recent firmware version is V1.54, releasing in mid December.

Others have answered many of your questions, let me give my shot at a few. I usually run my
KPA500 in contests at 600 watts. Briefly lighting the 700 watt LED is not unusual, but I don’t
consistently leave it lit. The amplifier is quite comfortable at 600 watts for long periods of time.
Mine is one of the first units and was hand-built, so I can’t claim to have the original PA Deck
installed (it is still sitting on my work bench however), but my current PA Deck is one of the
original shipping versions. After about 10 years, it is working just fine for me.

As for calibration, we perform the cal at the factory for factory-built units, but not for kits.
The reason is that we need to marry the front panel board with the PA Deck to perform these
adjustments, something that is not done until well into assembly. The adjustment values are
kept in memory on the front panel board’s processor. This also means that if you swap the
PA Deck you will need to recalibrate the measurements. Feel free to perform your own
calibration to a known standard. You will probably find that you will need to vary the values
by some small amount to get really accurate measurements. In general they are pretty close
to start off with, but won’t be “right on.”

Enjoy the amplifier, and by all means use it at the power you want. If you have any questions
or need any help, we are here, just ask. You will find customer support to be very helpful.

73!

Jack, W6FB
Elecraft Engineering

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Dennis Moore

Re: KPA500 Questions about power and efficiency

In reply to this post by KQ5S-Tom

Using the KPA Utility I just upgraded mine from 1.47 to 1.54, so it is
there.

73, Dennis NJ6G

On 1/16/2018 17:45, Tom-KQ5S wrote:
> "The most recent firmware version is V1.54, releasing in mid December."
>
> I went to the software page and it says the most recent beta release is MCU
> 1.52 Nov 17, 2017 and production release is 1.47.
>
> -----------------
> 73,
> Tom - KQ5S

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Dennis Moore

Re: KPA500 Questions about power and efficiency

But I agree, the Elecraft site does not show 1.54 as being available.

Dennis

On 1/16/2018 19:19, Dennis Moore wrote:
> Using the KPA Utility I just upgraded mine from 1.47 to 1.54, so it is
> there.
>
> 73, Dennis NJ6G

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Richard Lamont

Re: KPA500 Questions about power and efficiency

In reply to this post by Don Wilhelm

On 16/01/18 23:52, Don Wilhelm wrote:

> Bottom line, the Elecraft amplifiers will do maximum power at a 50% duty
> cycle all day long. You should reduce the power for long winded AM
> transmissions, but otherwise you can run maximum power.

If you're running AM, 500W PEP is what you get with 125W carrier and
100% modulation. Run over 125W carrier and you will flat top and
splatter. (In theory. I don't use AM so haven't tried it.)

73,
Richard G4DYA

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Michael Eberle

Re: KPA500 Firmware

In reply to this post by Dennis Moore

The KPA500 utility will find v1.54. It is on the website but without an
obvious link to it. You have to go to the beta FW folder
(ftp://ftp.elecraft.com/KPA/firmware/beta/) and then click "[parent
directory]" at the top of the page. There you will find the
KPA500FP0154.hex and the kpafwnotes.rtf for 1.54. I had to save the
kpafwnotes.rtf to my desktop and open it with Wordpad.

73, Mike KI0HA

On 1/16/2018 21:21, Dennis Moore wrote:

> But I agree, the Elecraft site does not show 1.54 as being available.
>
> Dennis
>
>
> On 1/16/2018 19:19, Dennis Moore wrote:
>> Using the KPA Utility I just upgraded mine from 1.47 to 1.54, so it
>> is there.
>>
>> 73, Dennis NJ6G
>
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>