There’s a mix of SMD and through-hole components on the custom-etched PCB, with a separate riser card to show off the VFDs a little bit through the front panel of the 3D printed case.

It is claimed a 2N3904 can achieve 500 pS rise times in this manner, something of an improvement on the 2N3904’s stock 35 nS mentioned above.

What is the 2N3904 transistor? According to 2N3904 datasheet this transistor is a silicon epitaxial planar NPN general purpose amplifier and switch. The ...