I also use this as a companion amp for my KX3. However purchasers should be aware that whereas the PTT line can be controlled from the Tx, and the relays are hard wired to respond to the changeover , the operating bias for the PA transistors remains RF switched. I had several complaints that my CW characters were received at two different signal strengths, a weak initial character, follwed by a stronger 'sound' as the RF activated transmit bias kicked in and the amp transistors suddenly amplified the incoming RF. Once I'd wired the operating bias to the PTT line, all was well.
Drive the amp with a maximum of 5 watts and you won't go wrong. The heat sink gets pretty warm and I had to retrofit two fans sucking air through the h/sink vanes and exhausting vertically. Do yourself a favour and buy the version with the two fans already fitted. All in all, an excellent companion amp and a good value for money, especially compared with the price of the Elecraft KXPA

What a fantastic little amp. Ideal for use with my ft-817 and my KX3. This is a gem of an amp. No need to run you radios at any power at all with this amp, 5 watts out of the 817 and its there. You will even have to turn your elecraft power down so you don't over drive this unit. And at full output powerit still produces a very nice clear signal with out any splatter.
The guys at the shop were more than helpful in guiding me to this amp explaining the full advantages of the band selector and the band pass filters inside. Even if you leave it on the automatic setting you won't be disappointed with its quick selection and performance.
And a brilliant 24hr turnaround from ordering to delivery. A Big Well Done