[Elecraft] Fwd: AW: K3 KPA3 bias adjust

[Bob McGraw K4TAX]

I just looked at the current values of my K3s using the internal DISP 
current and voltage values.

This is how it came from the factory after replacement of the KPA3A rev 
E amp on 5/30/2018.


In RX USB mode = 1.6A  Vcc = 13.8V  Audio volume at minimum.

In TX USB mode no audio,   10 watt PWR setting = 1.60A

In TX USB mode no audio, 100 watt PWR setting = 2.91A

The PWR delta is 1.31 amps


In RX CW mode,  = 1.03A   Vcc 13.8V   Audio volume at minimum.

In TX CW mode PTT closed, key open, 10 watt PWR setting 1.54A Vcc  13.7V

In TX XW mode, PTT closed, key open, 100 watt PWR setting 2.85A Vcc 13.6V

The PWR delta is 1.31 amps


Your values may be different if you have the 2nd receiver and can vary 
depending on your Vcc.

73

Bob, K4TAX


On 3/7/2019 12:34 PM, hawley, charles j jr wrote:
> Could you be mistaken on my procedure? The 1 amp plus or minus is typical with three K3s es that I know of. There are two devices and two trim pots.
>
> This instruction is only for one device since he says "the BIAS pot" I believe...
>
> " If there is much more current than this, set the BIAS pot to minimum
>   (fully counter clockwise). Then tap XMIT (not TUNE) and note what the
> current is in VFO B's readout. Slowly turn up the BIAS pot until you see
> 400-500mA more current that was seen with the BIAS pot at minimum."
>
> I am looking at the total current accessible from DISP and read out on the front panel. First I go to the LPA only, read the total current drawn by the rig under XMIT SSB(no modulation) and then engage the KPA by turning up the power knob and I subtract the first reading from the second. I get about 1.05 amps.
> Am I close to knowing the total current into the KPA this way?
>
> I feel that this important knowledge about how to set up the amp is fuzzy or not well known...the why I asked the question.
>
> Thanks for the replies!!
>
> Chuck Hawley
>   c-hawley at illinois.edu
>
>   Amateur Radio, KE9UW
>   aka Jack, BMW Motorcycles
>
> ________________________________
> From: Don Wilhelm <donwilh at embarqmail.com>
> Sent: Thursday, March 7, 2019 12:10 PM
> To: hawley, charles j jr; elecraft at mailman.qth.net; Mike Harris
> Subject: Re: [Elecraft] Fwd: AW: K3 KPA3 bias adjust
>
> Chuck,
>
> The instruction cited was for a 400-500 ma rise TOTAL (not per device).
> So I conclude your bias is set too high or there is a problem in the
> bias circuit.
>
> 73,
> Don W3FPR
>
> On 3/7/2019 9:31 AM, hawley, charles j jr wrote:
>> Thanks for the info. Using xmit for the low power amp and then going to the high power amp shows a difference of 1.05A. So my devices are showing about 500+ ma each. In the ball park.
>> Thanks so much for the reply.
>>
>> Chuck Hawley
>>    c-hawley at illinois.edu
>>
>>    Amateur Radio, KE9UW
>>    aka Jack, BMW Motorcycles
>>
>> ________________________________
>> From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> on behalf of Mike Harris via Elecraft <elecraft at mailman.qth.net>
>> Sent: Thursday, March 7, 2019 5:43 AM
>> To: elecraft at mailman.qth.net
>> Subject: [Elecraft] Fwd: AW: K3 KPA3 bias adjust
>>
>> Hi,
>>
>> Forwarded a 2009 email exchange for your info. I have NOT tried this so
>> use with care and at your own risk.
>>
>> Regards,
>>
>> Mike VP8NO
>>
>>
>> -------- Forwarded Message --------
>> Subject: AW: [Elecraft] K3 KPA3 bias adjust
>> Date: Sat, 3 Jan 2009 19:46:55 +0100
>> From: Koppendorfer Klaus <KK at ccf.net>
>> To: Jan Erik Holm <sm2ekm at telia.com>
>> CC: Elecraft at mailman.qth.net <Elecraft at mailman.qth.net>
>>
>> Locate the BIAS pot at the front of the KPA3, between the heat sink and
>> the KPA3 shield. Note what the display current is in the VFO B readout
>> when you tap the Display button and turn the VFO B knob to the current
>> readout. In RX, it should be 1.0A or so.   In XMIT (not TUNE), it should
>> be about 1.90 to 2.0A when the Power knob is set to 12w or above so the
>> KPA3 is made active (but there is no RF output since XMIT is used). Or
>> you can press the PTT button but do not speak.
>>
>> If there is much more current than this, set the BIAS pot to minimum
>> (fully counter clockwise). Then tap XMIT (not TUNE) and note what the
>> current is in VFO B's readout. Slowly turn up the BIAS pot until you see
>> 400-500mA more current that was seen with the BIAS pot at minimum.
>>
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