I have acquired what appears to be a vintage Crown amplifier when my brother passed away. It is a mono tube amp labeled as a "Crown GPA-25". It is a table top configuration and has 2 microphone volume knobs, a phono volume knob, bass and treble knobs, and an off/on switch (knob) on the front. Is anyone on here familiar with these? I've googled it and can find nothing about it. I'd really like to know more about it.