[Elecraft] KPA100 power on 20m/30m, update

[Geoffrey Mackenzie-Kennedy]

Hello Ted,

At the risk of continuing this thread for too long, brief comment.  IMHO you
hit on the main culprit causing problems on 20m / 30m - the inductance of
R19 and R20 as supplied.

If you like, I can go off list to discuss with you your other comments. I am
not surprised that you could not find evidence of other resonances, but
there are ways to expose them and they are an important part of a designer's
'toolkit'.   The important thing is that your problem has been solved.

73,

Geoff
GM4ESD


----- Original Message ----- 
From: "Ted Turk" <tedturk at fastnet.co.uk>
To: <elecraft at mailman.qth.net>
Sent: Friday, June 24, 2005 7:17 AM
Subject: Re: [Elecraft] KPA100 power on 20m/30m, update


> Geoff, Don,
>
> As an ex sufferer of this disease, my 2p worth.
>
> My investigations, admittedly only with the limited kit available to me
> including 20MHz scope and 2 or 3 different wattmeters, I think it was,
> showed that the output across all the bands up to 21MHz was remarkably
> constant for a given Q1,2 base voltage (and attempt at current
> calculation).  However, there was a very marked voltage (estimated
> current) loss across the base drive circuits on the affected bands
> (C80,81/R19,20).  Readings prior to this in the RF line merely
> confirmed the high drive requirement as did the Hi Cur on 20/30m.  With
> much help and advice from guys at my club, we too considered the
> possibility of other spurious resonant circuits but could find no
> evidence for these in my kit at a level that affected performance.
>
> 73,
> Ted G7BQM K2#4732 and first year RF engineering student!
>