This is a ruggedly built RC oscillator that covers the frequency range 15 Hz to 50 kHz. It can provide up to 1 watt into 600 Ω and up to 500 mW into 5 Ω.
The oscillator employs four thermionic valves, including a 6V6GT for the output stage and a 6X5GT full-wave rectifier..
This one is in reasonable cosmetic condition and works well.