AW: [Elecraft] Low power on 20m using the KPA100 option

[Renardy, Martin]

Hallo Vic,

Many thanks for the info. I thnink I am dealing with issue number 2).

By now I am quite shure that the driver part of KPA100 option is 
draining power on 20/30m avoiding the last stage to reach full
Power.

I am going to ask Gary.

Regards

Martin

-----Ursprüngliche Nachricht-----
Von: Vic Rosenthal [mailto:vic at rakefet.com] 
Gesendet: Montag, 6. Juni 2005 13:49
An: Renardy, Martin {GY-E~Mannheim}
Cc: elecraft at mailman.qth.net
Betreff: Re: [Elecraft] Low power on 20m using the KPA100 option


Renardy, Martin wrote:

> last weekend I finished the KPA100 option, which is causing a little 
> problem. Everything Is running well except power on 20m, where I just 
> reach 50 Watts.
> 
> The QRP output is not affected, so I am quite shure that the RF path 
> to the antenna through the LPF is ok. Just to be shure I have checked 
> all inductivities and capacities
> of the 20m filter. They are ok including the used core types of the
> inductivities.

If you are getting 10 watts output when you set the power control to 10 
watts, check the current draw at this power level by tapping Display. 
You should be drawing less than 3 amperes in this condition.  Check also 
at 11 watts, with the KPA100 on.  It shouldn't be much higher.  If it 
is, you may have problem (2) below.

I found two problems in my K2/100 which caused slightly (in my case) 
reduced output on 20 meters:

1) the bandpass filter tuning trimmers were both at maximum capacity. 
Adding a few pf in parallel with them allowed the QRP portion of the K2 
to develop more drive for the KPA100 with less current draw.

2) There is a known issue with some new KPA100s that the amplifier 
requires abnormally high drive on 20 and sometimes 30 meters.  This 
causes high current draw in the low-power stage and inability to reach 
full output.  Gary at Elecraft was helpful to me about this 
<support at elecraft.com>.

-- 
73
Vic, K2VCO
Fresno, CA
http://www.qsl.net/k2vco