Accessory4020391-09Synchronizes tape speed to film ory4010217-05/06Varies operatingI have only ever seen a few of these over past 25 years. Very rare unit. There were not many made, even fewer survived to this day Unit is a two stage push-pull Amplifier for broadcast studio from 1940s, which is highest standard Collins preamplifier ever built. It has input and output gain control at the Front panel. A pair of 6F8G easily accessible through a door in the front panel. Other components are easily reached by removing the dust cover. Input Impedance: 600 chms, or bridge with 20,000 ohms. 150 ohms available. Output Impedance: 600 ohms, 150 ohms available. Power Requirements: 6.3 volts l 0.6 amp. a-c or d-c. 100 to 250 volts cl-r. at 20 ma. Power may be obtained from the Collins 409T-1 or 409T-3 power supplies. It has not been powered up in many years. But all transformers check okay. Includes the original manual, which by itself is pretty rare.