KPA100 Low Power on 30m & 20m bands

[Barry Cooper - Relcom]

Hi,
I have completed the final alignment and test of my KPA100 amplifier which is working well in almost every respect other than relatively lower power output on the 30m and 20m bands. Measured power output is as follows:

80m 117W
40m 113W
30m 71W - initially flashes "Hi Cur" message
20m 75W - initially flashes "Hi Cur"
18m 105W
12m 103W
10m 99W

Power output measured at antenna socket across 50 ohm load using Tek scope and calulating Pwr = Vpp^2/400.
I have checked the inductors and capacitors in the two LPF chains. Everything appears ok, i.e. correct toroids used wound with correct number of turns. All capacitors check out as correct value with correct placement.
CAL CUR set at 3.5 as indicated in setup. Power output displayed on K2 matches calculated output power to within 2-3W. K2 running barefoot gives more than 10W on all bands.

Help please! Where do I look next?

Barry
G4RKO
K2 - 4703

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[Ted Turk]

Barry,

Hard luck but do not worry, you are not alone!  You are the third that
we know of in the UK and there was another in the USA.  Let Gary
Surrency at support know. In my case, a scope along the RF chain showed
that there were signal voltage (and estimated current) losses across
the base drive RC network to Q1,2 on the affected bands only.  The
problem has been temporarily cured by doubling the size of C80,81 in my
case and Larry's, G0IKE.

Elecraft are investigating and we are awaiting an explanation and cure.

73, Ted G7BQM K2 #4732

On 25 May 2005, at 08:35, Barry Cooper - Relcom wrote:

> Hi,
> I have completed the final alignment and test of my KPA100 amplifier
> which is working well in almost every respect other than relatively
> lower power output on the 30m and 20m bands. Measured power output is
> as follows:
>
> 80m 117W
> 40m 113W
> 30m 71W - initially flashes "Hi Cur" message
> 20m 75W - initially flashes "Hi Cur"
> 18m 105W
> 12m 103W
> 10m 99W
>
> Power output measured at antenna socket across 50 ohm load using Tek
> scope and calulating Pwr = Vpp^2/400.
> I have checked the inductors and capacitors in the two LPF chains.
> Everything appears ok, i.e. correct toroids used wound with correct
> number of turns. All capacitors check out as correct value with
> correct placement.
> CAL CUR set at 3.5 as indicated in setup. Power output displayed on K2
> matches calculated output power to within 2-3W. K2 running barefoot
> gives more than 10W on all bands.
>
> Help please! Where do I look next?
>
> Barry
> G4RKO
> K2 - 4703
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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