The step from 12 to 100 Watts.

The government and the CBers pretty much eliminated manufacture and sale of amplifiers for QRP radios 30 years ago.  However the law did not stop the proliferation of high power CB amps, but ended commercial QRP amps for Hams .  This has recently changed and Ten Tec is making a 100 Watt QRP amp now for its new Argonaut rig.  I tried one and was not happy with it.  The HLA 150 cost less than 1/2 as much as the Ten Tec 418, and works much better.

Since the KX3's max power is 12 Watts and the radio gods are mistreating us,  I use an RM Italy HLA (Ham Linear Amplifier) 150, Plus (fan cooled), sitting on an MFJ tuner sitting on a shelf over the computer screen.  Both have been modified, the tuner for quality and use and the amp for use (it's quality is very good).  The amp has had a switch added to turn off the cooling fans, which are normally on low setting all the time.  In SSB and CW modes just using 100 Watts, the amp doesn't need the fans at all (you might consider the cheaper fan less model). However if you want to run RTTY or any other full duty cycle mode, the fan is needed.  I like the silence when possible...a signal to noise ratio improvement for the shack. The thermometer was added to see what the limits on the internal fan controller were. Besides it's a good place to keep it.  I can't say it makes it look cool, because the amp is butt ugly, so much for Italian radio design.  They do much better with cars and actresses. 

This amp has a big problem. First of all, it is not FCC type certified, probably because it is over rated.  They claim it to be 150 Watts (which is possible, even with just 2 to 5 Watts drive), but it's IMD output is unacceptable at this level.  The low pass filters work very well, and the amp puts out a good  clean signal with a 13 to 15V power supply at the 100 Watts or less.  I have added a 4.4 Farad capacitor (thank you mobile audio nuts) to the power input to further guarantee the voltage stability.  It can be seen reading 13.6V in the background of the pix.  The MFJ tuner has had a bypass switch added and some basic internal repair and soldering like most of their products need to produce a competent piece of equipment.  It is usually in bypass mode.  I must limit my power out put to 100 Watts so I don't over drive my SGC 230 auto tuners.

Many Hams are leery of using an amplifier that is not FCC certified, however, certification is not a problem for the Ham operator, its a problem for the importer and retailer.  Since Hams are licensed to build and use their own amplifiers, they can certainly use one that has not been certified.  The Ham is responsible for the transmitted signal that radiates from his antenna.  I have tested my radiated signal with this amp at the 100 Watt level and find that the first order IMD is down over 40dB, noticeably better than my certified Yaesu FT 857.  The HLA-150 can be purchased here: http://www.dnjradio.com/DNJRadio_Catalog_2011.pdf