I picked up a '50s HP 120B oscilloscope for $15 on Craigslist. I wonder if it works?

Whole lotta tubey goodness inside

Tubes closeup

More tubes

It works! Here's a sine wave running through the Cow Pi amp, with volume controls set to a clean, undistorted level

As I turn up the master volume, the power tube clipping becomes evident

Turning it up more

Maximum volume. Not really a sine wave anymore. Distortion!

Examining a square wave coming from a signal generator app on my phone. Not very square

Viewing the built-in calibration signal. Also not very square