Elecraft

K2: KPA100 fan issue + current question

Classic

List

Threaded

12 messages Options

Jim KO5V

K2: KPA100 fan issue + current question

Well, after checking that all of the components in the fan circuit were correct, I decided to follow Don's usual advice about checking my soldering, so I re-flowed all of their joints. None looked bad, but now the fan works as it should, so...

I'm still curious about my 11A @ 100W measurement. I think I'll borrow a friend's DMM and see if I get the same voltage measurement across R1
(unless 11A is in the ballpark).

73, Jim KO5V

-----Forwarded Message-----

>From: Jim KO5V <[hidden email]>
>Sent: Nov 8, 2018 2:11 PM
>To: Elecraft List <[hidden email]>
>Subject: K2: KPA100 fan issue + current question
>
>I just finished building and testing the KPA100 that goes with K2 #7225. This kit was a rev C, and I have brought it up to the latest specs. U1 says PA 1.1.
>
>#1: It has passed all of the tests, except it apparently has no low fan speed. I have set the temperature of the heat sink using CAL tPA, after measuring it with an IR thermometer, and I have set and re-set the fan parameters in the secondary menu. On "nor" and on "LoHi" the fan is off. On "Hi" it runs. I have tested the amp's output into my power meter at 100w, but I haven't transmitted long enough to really heat anything up.
>
>When I first applied power to the KPA100 for the initial tests, I believe the fan ran at low speed, so I have probably broken something...
>
>#2: When I key the amp at 100w, through the power meter, and into a dummy load, I measure about .055v across R7, so that's ~11A. I expected higher current. Does that seem about right?
>
>Any insight would be appreciated.
>
>Thanks in advance, & 73,
>
>Jim KO5V

______________________________________________________________
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: K2: KPA100 fan issue + current question

Jim,

I would expect that the current at 100 watts would be closer to 17 or 18
amps.
Has the bias been set correctly for a 400mA rise in PA current with no
RF input? That bias setting will alter the operating class of the
amplifier and it must be correct to be linear.

73,
Don W3FPR

On 11/9/2018 11:46 AM, Jim KO5V wrote:
> Well, after checking that all of the components in the fan circuit were correct, I decided to follow Don's usual advice about checking my soldering, so I re-flowed all of their joints. None looked bad, but now the fan works as it should, so...
>
> I'm still curious about my 11A @ 100W measurement. I think I'll borrow a friend's DMM and see if I get the same voltage measurement across R1
> (unless 11A is in the ballpark).
______________________________________________________________
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]

Jim KO5V

Re: K2: KPA100 fan issue + current question

In reply to this post by Jim KO5V

Don,

Yes, I set the bias as described, and at that setting, R6 is rotated about 1/3 clockwise from fully CCW (I saw a reference to that reference in the archives). My guess is that my 35 year-old Beckman meter may be having trouble measuring small voltages, so I'll try another meter, and I'll report what I find.

Thanks!

73, Jim KO5V

-----Original Message-----

>From: Don Wilhelm <[hidden email]>
>Sent: Nov 9, 2018 9:56 AM
>To: Jim KO5V <[hidden email]>, Elecraft List <[hidden email]>
>Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>
>Jim,
>
>I would expect that the current at 100 watts would be closer to 17 or 18
>amps.
>Has the bias been set correctly for a 400mA rise in PA current with no
>RF input? That bias setting will alter the operating class of the
>amplifier and it must be correct to be linear.
>
>73,
>Don W3FPR
>
>On 11/9/2018 11:46 AM, Jim KO5V wrote:
>> Well, after checking that all of the components in the fan circuit were correct, I decided to follow Don's usual advice about checking my soldering, so I re-flowed all of their joints. None looked bad, but now the fan works as it should, so...
>>
>> I'm still curious about my 11A @ 100W measurement. I think I'll borrow a friend's DMM and see if I get the same voltage measurement across R1
>> (unless 11A is in the ballpark).

Bob McGraw - K4TAX

Re: K2: KPA100 fan issue + current question

In reply to this post by Jim KO5V

At 13.8 volts, 11amps is about 152 watts input. 100/152 = .658 * 100 for about 66% efficiency.

All in all , looks about right to me. AKA - I wouldn't be concerned.

Bob, K4TAX

Sent from my iPhone

> On Nov 9, 2018, at 10:46 AM, Jim KO5V <[hidden email]> wrote:
>
> Well, after checking that all of the components in the fan circuit were correct, I decided to follow Don's usual advice about checking my soldering, so I re-flowed all of their joints. None looked bad, but now the fan works as it should, so...
>
> I'm still curious about my 11A @ 100W measurement. I think I'll borrow a friend's DMM and see if I get the same voltage measurement across R1
> (unless 11A is in the ballpark).
>
> 73, Jim KO5V
>
> -----Forwarded Message-----
>> From: Jim KO5V <[hidden email]>
>> Sent: Nov 8, 2018 2:11 PM
>> To: Elecraft List <[hidden email]>
>> Subject: K2: KPA100 fan issue + current question
>>
>> I just finished building and testing the KPA100 that goes with K2 #7225. This kit was a rev C, and I have brought it up to the latest specs. U1 says PA 1.1.
>>
>> #1: It has passed all of the tests, except it apparently has no low fan speed. I have set the temperature of the heat sink using CAL tPA, after measuring it with an IR thermometer, and I have set and re-set the fan parameters in the secondary menu. On "nor" and on "LoHi" the fan is off. On "Hi" it runs. I have tested the amp's output into my power meter at 100w, but I haven't transmitted long enough to really heat anything up.
>>
>> When I first applied power to the KPA100 for the initial tests, I believe the fan ran at low speed, so I have probably broken something...
>>
>> #2: When I key the amp at 100w, through the power meter, and into a dummy load, I measure about .055v across R7, so that's ~11A. I expected higher current. Does that seem about right?
>>
>> Any insight would be appreciated.
>>
>> Thanks in advance, & 73,
>>
>> Jim KO5V
> ______________________________________________________________
> 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]
>

Jim KO5V

Re: K2: KPA100 fan issue + current question

In reply to this post by Jim KO5V

Thanks Bob,

That makes me feel a bit better. I'm still going to remeasure it with a newer meter and see if the measurements check.

73, Jim KO5V

-----Original Message-----

>From: Bob McGraw K4TAX <[hidden email]>
>Sent: Nov 9, 2018 10:29 AM
>To: Jim KO5V <[hidden email]>
>Cc: Elecraft List <[hidden email]>
>Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>
>At 13.8 volts, 11amps is about 152 watts input. 100/152 = .658 * 100 for about 66% efficiency.
>
>All in all , looks about right to me. AKA - I wouldn't be concerned.
>
>
>Bob, K4TAX
>
>
>Sent from my iPhone
>
>> On Nov 9, 2018, at 10:46 AM, Jim KO5V <[hidden email]> wrote:
>>
>> Well, after checking that all of the components in the fan circuit were correct, I decided to follow Don's usual advice about checking my soldering, so I re-flowed all of their joints. None looked bad, but now the fan works as it should, so...
>>
>> I'm still curious about my 11A @ 100W measurement. I think I'll borrow a friend's DMM and see if I get the same voltage measurement across R1
>> (unless 11A is in the ballpark).
>>
>> 73, Jim KO5V
>>
>> -----Forwarded Message-----
>>> From: Jim KO5V <[hidden email]>
>>> Sent: Nov 8, 2018 2:11 PM
>>> To: Elecraft List <[hidden email]>
>>> Subject: K2: KPA100 fan issue + current question
>>>
>>> I just finished building and testing the KPA100 that goes with K2 #7225. This kit was a rev C, and I have brought it up to the latest specs. U1 says PA 1.1.
>>>
>>> #1: It has passed all of the tests, except it apparently has no low fan speed. I have set the temperature of the heat sink using CAL tPA, after measuring it with an IR thermometer, and I have set and re-set the fan parameters in the secondary menu. On "nor" and on "LoHi" the fan is off. On "Hi" it runs. I have tested the amp's output into my power meter at 100w, but I haven't transmitted long enough to really heat anything up.
>>>
>>> When I first applied power to the KPA100 for the initial tests, I believe the fan ran at low speed, so I have probably broken something...
>>>
>>> #2: When I key the amp at 100w, through the power meter, and into a dummy load, I measure about .055v across R7, so that's ~11A. I expected higher current. Does that seem about right?
>>>
>>> Any insight would be appreciated.
>>>
>>> Thanks in advance, & 73,
>>>
>>> Jim KO5V
>> ______________________________________________________________
>> 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: K2: KPA100 fan issue + current question

Jim,

That 11 amps would sound more reasonable to me if you can say that the
base K2 is being powered separately, but I would expect something closer
to 50% efficiency rather than 66%.

73,
Don W3FPR

On 11/9/2018 12:42 PM, Jim KO5V wrote:

> Thanks Bob,
>
> That makes me feel a bit better. I'm still going to remeasure it with a newer meter and see if the measurements check.
>
> 73, Jim KO5V
>
>
> -----Original Message-----
>> From: Bob McGraw K4TAX <[hidden email]>
>> Sent: Nov 9, 2018 10:29 AM
>> To: Jim KO5V <[hidden email]>
>> Cc: Elecraft List <[hidden email]>
>> Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>>
>> At 13.8 volts, 11amps is about 152 watts input. 100/152 = .658 * 100 for about 66% efficiency.
>>
>> All in all , looks about right to me. AKA - I wouldn't be concerned.
>>
>>
>> Bob, K4TAX
>>
>>

Elecraft mailing list

Re: K2: KPA100 fan issue + current question

Efficiency is an interesting point in a linear amplifier. As the linear is “efficiency” modulated when it is driven to full power output it does in fact approach the 70% efficiency level of a class C amplifier. Not quite but it closes in. The 30% to 50% rating a linear amplifier normally receives is more of an average number which approximates the SSB talking power efficiency.

Very 73 - Mike - K9JRI

> On Nov 9, 2018, at 1:37 PM, Don Wilhelm <[hidden email]> wrote:
>
> Jim,
>
> That 11 amps would sound more reasonable to me if you can say that the base K2 is being powered separately, but I would expect something closer to 50% efficiency rather than 66%.
>
> 73,
> Don W3FPR
>

______________________________________________________________
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]

Jim KO5V

Re: K2: KPA100 fan issue + current question

In reply to this post by Jim KO5V

Don and Bob,

The K2 and amp are both powered from the amp's supply.

I used a known good DVM to measure the voltage across R7, and it agrees with old Beckman. I now think my old kit-built Ten Tec power meter may be badly out of calibration. I have a dead LP-100 that is on its way back to Larry for upgrade and calibration, so I'll just wait until it is back to finish calibrating the KPA's power setting.

Here are what I measured and calculated at the approximate center of each band, in cw, when the K2's LCD read 100W:

10M: .067V, 13.4A
12M: .049V, 9.8A
15M: .064V, 12.8A
17M: .065V, 13A
20M: .048V, 9.6A
30M: .056V, 11.2A
40M: .052V, 10.4A
60M: .056V, 11.2A
80M: .054V, 10.8A

The current seems to vary significantly between bands, but maybe that's normal?

Thanks again. 73,

Jim KO5V

-----Original Message-----

>From: Don Wilhelm <[hidden email]>
>Sent: Nov 9, 2018 11:37 AM
>To: Jim KO5V <[hidden email]>, Bob McGraw K4TAX <[hidden email]>, Elecraft List <[hidden email]>
>Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>
>Jim,
>
>That 11 amps would sound more reasonable to me if you can say that the
>base K2 is being powered separately, but I would expect something closer
>to 50% efficiency rather than 66%.
>
>73,
>Don W3FPR
>
>On 11/9/2018 12:42 PM, Jim KO5V wrote:
>> Thanks Bob,
>>
>> That makes me feel a bit better. I'm still going to remeasure it with a newer meter and see if the measurements check.
>>
>> 73, Jim KO5V
>>
>>
>> -----Original Message-----
>>> From: Bob McGraw K4TAX <[hidden email]>
>>> Sent: Nov 9, 2018 10:29 AM
>>> To: Jim KO5V <[hidden email]>
>>> Cc: Elecraft List <[hidden email]>
>>> Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>>>
>>> At 13.8 volts, 11amps is about 152 watts input. 100/152 = .658 * 100 for about 66% efficiency.
>>>
>>> All in all , looks about right to me. AKA - I wouldn't be concerned.
>>>
>>>
>>> Bob, K4TAX
>>>
>>>

Don Wilhelm

Re: K2: KPA100 fan issue + current question

Jim,

That is normal. The Transmit RF Gain varies from band to band, and that
will cause the current draw to vary. I am surprised that 12M is so low,
it is normally on a par with 10 meters.

Part of the RF Gain variation is in the base K2 and some more of it is
in the KPA100.

Remember that those are steady state current draws. The dynamic current
such as with SSB operation may peak at greater than what you measured.

Yes, use the LP-100 for calibrating the KPA100 wattmeter. Since the
LP-100 has NIST traceable calibration, I would believe it over the
readings on a calibrated BIRD.

73,
Don W3FPR

On 11/9/2018 5:56 PM, Jim KO5V wrote:

Jim KO5V

Re: K2: KPA100 fan issue + current question

In reply to this post by Jim KO5V

Thanks again, Don.

It's good to know that the variation in current isn't a problem. I was also a bit surprised with the 12M and 20M measurements.

I think I will do a complete realignment of the K2, and set up the wattmeter on the KPA when I get the LP100 back. Meanwhile, I'll try a few QSOs at 50W or so and see what happens.

73, Jim KO5V

-----Original Message-----

>From: Don Wilhelm <[hidden email]>
>Sent: Nov 9, 2018 5:15 PM
>To: Jim KO5V <[hidden email]>, Bob McGraw K4TAX <[hidden email]>, Elecraft List <[hidden email]>
>Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>
>Jim,
>
>That is normal. The Transmit RF Gain varies from band to band, and that
>will cause the current draw to vary. I am surprised that 12M is so low,
>it is normally on a par with 10 meters.
>
>Part of the RF Gain variation is in the base K2 and some more of it is
>in the KPA100.
>
>Remember that those are steady state current draws. The dynamic current
>such as with SSB operation may peak at greater than what you measured.
>
>Yes, use the LP-100 for calibrating the KPA100 wattmeter. Since the
>LP-100 has NIST traceable calibration, I would believe it over the
>readings on a calibrated BIRD.
>
>73,
>Don W3FPR
>
>On 11/9/2018 5:56 PM, Jim KO5V wrote:
>> Don and Bob,
>>
>> The K2 and amp are both powered from the amp's supply.
>>
>> I used a known good DVM to measure the voltage across R7, and it agrees with old Beckman. I now think my old kit-built Ten Tec power meter may be badly out of calibration. I have a dead LP-100 that is on its way back to Larry for upgrade and calibration, so I'll just wait until it is back to finish calibrating the KPA's power setting.
>>
>> Here are what I measured and calculated at the approximate center of each band, in cw, when the K2's LCD read 100W:
>>
>> 10M: .067V, 13.4A
>> 12M: .049V, 9.8A
>> 15M: .064V, 12.8A
>> 17M: .065V, 13A
>> 20M: .048V, 9.6A
>> 30M: .056V, 11.2A
>> 40M: .052V, 10.4A
>> 60M: .056V, 11.2A
>> 80M: .054V, 10.8A
>>
>> The current seems to vary significantly between bands, but maybe that's normal?
>>
>>
>

Bob McGraw - K4TAX

Re: K2: KPA100 fan issue + current question

In reply to this post by Jim KO5V

Not at all unusual for the currents to be different on different bands.

Since most power meters are voltage sensing devices, the value of the
dummy load will affect the power indication. Thus as the R value
increases the voltage across the R increases for a given power value and
thus the meter will indicate more power than actually exists.   And the
better power meters are typically +/- 5% full scale, i.e. Bird 43.
Many ham meters are +/- 10%.   The LP-100 is +/- 3% with NIST factory
calibration.

As to dummy loads, I have 3 and they all say 50 ohms on the label. In
fact they measure between 48 ohms and 54 ohms when cold. The value goes
up as the element and radiator heats.   While that's not much, in fact
it is approaching 10%.    That throws another variable in power
measurements.

I stopped frettin' over power values a long long time ago.

73
Bob, K4TAX

On 11/9/2018 4:56 PM, Jim KO5V wrote:

> Don and Bob,
>
> The K2 and amp are both powered from the amp's supply.
>
> I used a known good DVM to measure the voltage across R7, and it agrees with old Beckman. I now think my old kit-built Ten Tec power meter may be badly out of calibration. I have a dead LP-100 that is on its way back to Larry for upgrade and calibration, so I'll just wait until it is back to finish calibrating the KPA's power setting.
>
> Here are what I measured and calculated at the approximate center of each band, in cw, when the K2's LCD read 100W:
>
> 10M: .067V, 13.4A
> 12M: .049V, 9.8A
> 15M: .064V, 12.8A
> 17M: .065V, 13A
> 20M: .048V, 9.6A
> 30M: .056V, 11.2A
> 40M: .052V, 10.4A
> 60M: .056V, 11.2A
> 80M: .054V, 10.8A
>
> The current seems to vary significantly between bands, but maybe that's normal?
>
> Thanks again. 73,
>
> Jim KO5V
>
>
>
> -----Original Message-----
>> From: Don Wilhelm <[hidden email]>
>> Sent: Nov 9, 2018 11:37 AM
>> To: Jim KO5V <[hidden email]>, Bob McGraw K4TAX <[hidden email]>, Elecraft List <[hidden email]>
>> Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>>
>> Jim,
>>
>> That 11 amps would sound more reasonable to me if you can say that the
>> base K2 is being powered separately, but I would expect something closer
>> to 50% efficiency rather than 66%.
>>
>> 73,
>> Don W3FPR
>>
>> On 11/9/2018 12:42 PM, Jim KO5V wrote:
>>> Thanks Bob,
>>>
>>> That makes me feel a bit better. I'm still going to remeasure it with a newer meter and see if the measurements check.
>>>
>>> 73, Jim KO5V
>>>
>>>
>>> -----Original Message-----
>>>> From: Bob McGraw K4TAX <[hidden email]>
>>>> Sent: Nov 9, 2018 10:29 AM
>>>> To: Jim KO5V <[hidden email]>
>>>> Cc: Elecraft List <[hidden email]>
>>>> Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>>>>
>>>> At 13.8 volts, 11amps is about 152 watts input. 100/152 = .658 * 100 for about 66% efficiency.
>>>>
>>>> All in all , looks about right to me. AKA - I wouldn't be concerned.
>>>>
>>>>
>>>> Bob, K4TAX
>>>>
>>>>

Jim KO5V

Re: K2: KPA100 fan issue + current question

In reply to this post by Jim KO5V

Thanks Bob,

Yet another variable! I just measured my dummy load at 54 ohms (cold). Maybe I should just declare victory and move on!

73, Jim KO5V

-----Original Message-----

>From: Bob McGraw K4TAX <[hidden email]>
>Sent: Nov 9, 2018 8:51 PM
>To: Jim KO5V <[hidden email]>, [hidden email], Elecraft List <[hidden email]>
>Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>
>Not at all unusual for the currents to be different on different bands.
>
>Since most power meters are voltage sensing devices, the value of the
>dummy load will affect the power indication. Thus as the R value
>increases the voltage across the R increases for a given power value and
>thus the meter will indicate more power than actually exists.   And the
>better power meters are typically +/- 5% full scale, i.e. Bird 43.
>Many ham meters are +/- 10%.   The LP-100 is +/- 3% with NIST factory
>calibration.
>
>As to dummy loads, I have 3 and they all say 50 ohms on the label. In
>fact they measure between 48 ohms and 54 ohms when cold. The value goes
>up as the element and radiator heats.   While that's not much, in fact
>it is approaching 10%.    That throws another variable in power
>measurements.
>
>I stopped frettin' over power values a long long time ago.
>
>73
>Bob, K4TAX
>
>
>
>On 11/9/2018 4:56 PM, Jim KO5V wrote:
>> Don and Bob,
>>
>> The K2 and amp are both powered from the amp's supply.
>>
>> I used a known good DVM to measure the voltage across R7, and it agrees with old Beckman. I now think my old kit-built Ten Tec power meter may be badly out of calibration. I have a dead LP-100 that is on its way back to Larry for upgrade and calibration, so I'll just wait until it is back to finish calibrating the KPA's power setting.
>>
>> Here are what I measured and calculated at the approximate center of each band, in cw, when the K2's LCD read 100W:
>>
>> 10M: .067V, 13.4A
>> 12M: .049V, 9.8A
>> 15M: .064V, 12.8A
>> 17M: .065V, 13A
>> 20M: .048V, 9.6A
>> 30M: .056V, 11.2A
>> 40M: .052V, 10.4A
>> 60M: .056V, 11.2A
>> 80M: .054V, 10.8A
>>
>> The current seems to vary significantly between bands, but maybe that's normal?
>>
>> Thanks again. 73,
>>
>> Jim KO5V
>>
>>
>>
>> -----Original Message-----
>>> From: Don Wilhelm <[hidden email]>
>>> Sent: Nov 9, 2018 11:37 AM
>>> To: Jim KO5V <[hidden email]>, Bob McGraw K4TAX <[hidden email]>, Elecraft List <[hidden email]>
>>> Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>>>
>>> Jim,
>>>
>>> That 11 amps would sound more reasonable to me if you can say that the
>>> base K2 is being powered separately, but I would expect something closer
>>> to 50% efficiency rather than 66%.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> On 11/9/2018 12:42 PM, Jim KO5V wrote:
>>>> Thanks Bob,
>>>>
>>>> That makes me feel a bit better. I'm still going to remeasure it with a newer meter and see if the measurements check.
>>>>
>>>> 73, Jim KO5V
>>>>
>>>>
>>>> -----Original Message-----
>>>>> From: Bob McGraw K4TAX <[hidden email]>
>>>>> Sent: Nov 9, 2018 10:29 AM
>>>>> To: Jim KO5V <[hidden email]>
>>>>> Cc: Elecraft List <[hidden email]>
>>>>> Subject: Re: [Elecraft] K2: KPA100 fan issue + current question
>>>>>
>>>>> At 13.8 volts, 11amps is about 152 watts input. 100/152 = .658 * 100 for about 66% efficiency.
>>>>>
>>>>> All in all , looks about right to me. AKA - I wouldn't be concerned.
>>>>>
>>>>>
>>>>> Bob, K4TAX
>>>>>
>>>>>
>
>