Glowbug is the term given to describe Amateur Radio operators (HAM) and sometimes their equipment because of their fondness for vacuum tube electronics.  This cute little toy oscilloscope is completely operational and uses vacuum tubes to drive its 7cm CRT. The casing is wood, and the brass fittings add a nice touch. This is actually a Mark II variant of an earlier design.

The schematic shows a pretty simple, yet brilliant pentode-based circuit, and the engineer is happy to explain the circuit in stunning detail.  I could build one in my sleep after many hours of lost sleep:

It uses three different small-signal rf pentodes – an EF91 in the timebase circuit, an EF184 in the Y amplifier, and an EF80 in the X amplifier.  The choice of tubes is somewhat arbitrary. The EF91 would be very suitable in all three functions since, among small-signal pentodes, it is unusual in having suitable characteristics for providing a relatively large anode voltage swing with little distortion.  But I do not find the EF91 visually attractive, so I opted for the other tubes in the main functions, relegating the ’91 to the back of the chassis, where its smaller size fits in nicely.  The EF184 has high transconductance, so is used in the Y amplifier where large voltage gain is required, while the EF80 is used with cathode-degeneration feedback in the X amplifier which requires much less gain, but a larger voltage output with good linearity.

Details: http://g4oep.atspace.com/toycro/toycro.htm#Mark II version with Added Brass [broken link]