Vintage Grebe MU-1 Synchrophase vacuum tube radio receiver With Gold-Plated Escutcheons, Battery Operation, Circa 1925. This was a 5 tube tuned radio frequency (TRF) receiver with two stages of radio frequency amplification, a grid-leak detector stage, and two audio amplifier stages. The 3 tuning dials had to be tuned in unison, so Grebe used thumbwheels that could be turned with a finger, so a third hand was not needed. Alternatively they could be linked together with the chain drive visible and turned with one knob.