Date: Thu, 8 Jul 2021 14:50:40 -0400
From: <john@kk9a.com>
To: <amps@contesting.com>
Subject: Re: [Amps] FT8 power with the KPA1500
<From an amplifier heating standpoint it probably makes very little
<difference what power level you use with an Elecraft KPA1500. See the
<Elecraft post on efficiency in the link below. I am not an amp guru but I
<believe SPE Expert amps have different PA voltages which increases their
<lower power efficiency.
<http://mailman.qth.net/pipermail/elecraft/2018-August/259502.html
<73,
<John KK9A
### Per the link above, the KPA-1500 only makes 51.9% eff at 1.5 kw
output. The german B26 amp is 70% eff at 1.5 kw. Similar eff for the uk
amp. That's a HUGE difference. Linear amplifiers are also known
as...variable eff amplifiers. IE: max eff at max PO. The eff on the uk
ss amp drops like a rock when run at lower powers, hence the 27/36/48 vdc
options. That allows for max eff at 500/ 900 w po levels...and much
reduced dissipation.
## The reason the diss is similar at lower po's, vs higher po's on the
KPA-1500 is because the eff never exceeds 51.9% at it's very best.
## for data / rtty/ FM useage, reducing the idling current a bunch would
be a huge asset. Idle current does not have to be cut off completely
either, just reduced to a very low value. The same thing can easily be
done with tube amps. One caveat though with GG triode tube amps when
operating CW. The idle current can not be reduced to zero, otherwise you
will get key clicks. But it can easily be reduced to 10 ma. Idle current
can be reduced to zero..and biased to class C, for FM.
## on my L4B's, drake used zero bias, and idle current is 220 ma. I
added adjustable bias..and redued the idle current down to just 100 ma on
the 2650 vdc mode....and just 40 ma on the 1900 vdc mode. Linearity did not
change, it could probably be reduced even further. I will test that theory
at a later date.
Jim VE7RF
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