Here's a nice little solid state amp for headphone use or a small 4Ω speaker. Good candidate for a bench top amp for testing purposes. You can board mount the pot and it will fit in a 1590A just fine.
This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.