Jen was an Italian manufacturer in the 60s and 70s that produced their own line of effects in addition to OEM stuff for other brands like Gretsch and Vox. This fuzz effect is essentially a Fuzz Face with an emitter follower up front and clipping diodes on the output. It produces a treble-heavy fuzz with a good bit of volume. Original transistors were BC238B for Q1-2 and a BC239C for Q3. Some schematics floating around call for 2N5088s, but shoot for transistors in the 200hFE range (2N2222, 2N3904, etc). This layout should fit in a 1590A, and if you drill the enclosure right, you could board-mount the pots using long-leg right angle PCB pots (mounted from the component side).
