Oscillograph - Side View
Here is the Clough-Brengle with the cover removed. The cathode ray tube can be seen stretching across almost the entire length. Unfortunately this tube is a later replacement, a 3AP1. The original would have been an RCA type 906 which had a very cool clear envelope; it lacked the aquadag coating used in the 3AP1.
The very round vacuum tube resting near the power transformers is a type 81 half-wave rectifier tube. Usually these are in envelopes with "shoulders," like the other tubes visible in the center. This must be an early example.
Unfortunately there is quite a bit of rust on the rear part of the chassis, probably caused by an incontinent electrolytic capacitor. The likely candidate skulks behind some other parts...