A number of constructors have eyed up adding an afterburner to their µBITx. The usual cautions apply: make sure your µBITx has clean output with earlier v3 and v4 boards having been upgraded to remove harmonics and spurs, before even considering adding a power amplifier.
There are a range of cheap Chinese and Russian kits available to give you between 40w and 70w output. However, these may be better avoided, since you can build a WA2EBY power amplifier without a lot of effort. This is a very solid design, and well proven.
Some list members suggested it may be hard to source boards for this amplifier design. However, take a look at:
http://www.golddredgervideo.com/kc0wox/wa2ebyamp/ (pointer to availability of boards) and
http://diycrap.blogspot.com/2016/06/wa2eby-irf510-amplifier.html and
http://kit-projects.com/AMP.en-us.htm
Allison KB1GMX commented:
Its a good design and allows for getting good performance at higher frequencies. Mine with a little effort does 37W on 10M (1.8W drive) and with the same drive at 40M about 55W. 80 and 20 are about 50. Never though to try 15 or 17m but I’d expect about 44w. The 1.8W is because I use an attenuator at the amp input as most of my HB radios do 4W which is excessive power or the amp. FYI I run it at 28V.
It is a good amp. Mine is now 13 years old and still running the same set of IRF510s. I did use a large heatsink (4×8″ with 1″ fins and the base thickness was .300″). Some call it overkill, but with no fan running and with a brick on the key for 10 minutes, the amp doesn’t fail.
At least one of the “70W DIY AMP” I’ve seen did produce that much power for about 1 minute into a dummy load before it blew up. Failure was likely due to self oscillation or overheating of the supplied heatsink. The heatsink was maybe pentium II vintage with mounting points for
a fan and not at all large or having many fins.
https://amateurradiokits.in/product/hf-linear-amp-40-watts/
MVS Sarma also points out that Sunil VU3SUA sells a set of black masked PCBs for the WA2EBY amplifier.