I just picked this up on FBM, and after some contact cleaner, it's working okay - clean/bright/sharp trace, controls all work, etc. Enough to tell me that it's worth fully fixing up.
It's got one real functional issue. Adjusting the vertical amplitude via the vernier expands the trace as expected, but also moves the trace's position.
It's a pretty complex three-stage differential setup, with direct coupling and cross-coupled plate-grid feedback. The service manual just says to investigate the vertical amplifier ... Uh, thanks I guess? I know my common-cathode stuff, but not a lot about differential amplifiers. The 12AU7s test a little weak, but still serviceable (and I don't have any spares on hand anyway).
Before I dive into thoroughly analyzing the circuit, any quick ideas I should try?
(I'll also mention that vertical sensitivity isn't great, and LF response isn't that hot either. The calibration trace is awfully slopey. I suspect these are all related issues.)