Hallicrafters FPM-200

The PTO's

Those wonderfully stable and accurate PTO's. As you can see these are original as is evident by their sequential serialization as R013 (Right) and L014 (Left). Just like the PTO's found in early Collins gear each PTO has three identical drying decantors located in small glass cylinders at the top.

Each PTO tunes a 500kc spread from 8.25 to 8.75Mc. PTO selection is via solid-state diode switching. There is a PTO-front mounted potentiometer which is gear driven along with the PTO tuning inductor that provides a DC voltage to varicaps in the RF stages of the receiver and transmitter sections. As a result the RF stages track along with the tuning. Talk about COOL! Externally each PTO also has one small variable capacitor which allow for calibration correction of the PTO. These are adjusted to set the frequency for the center of the band. Internal to each PTO is a small variable capacitor which provides for temperature compensation. Since both PTO's in this rig were found to be very stable over time and temperature, no attempt was made to open the PTO's to make such an adjustment. I believe that it is best to leave things alone if they are working fine!