I use the PL4 to drive my Mids/Twts, I use a class D for bass drivers.
Its EL34 Output Tubes are ideal for the task.
I really liked its performance, but noticed some cheap parts under the hood, I decided to upgrade a few caps and resistors in key locations.
Nothing to flash, just changed the Chinese film caps to a reputable make and some key resistors from MOX to Metal Film and Carbon Film.





It didn't make a massive difference, but then I did say it performed well as stock. The mods subtly increased the body and richness of the mids, down into the crossover range of the bass.
Slight gain in transparency and fine detail.
For the relatively small outlay it was worth the effort.

If your interested, see the full story on my blog, you can find schematics for the ProLogue One and Prologue Four there.
https://www.jkwynn.co.uk/PL4/PL4_03.html