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820K/r AM TrniisiniHers

Collins 820E/F-1 series of broadcast transmitters is one of the most extensively transistorized series of transmitters available in the 5-kW to 10 kW power rangę. The series feature solid State devices in Iow level audio and driver, power supply circuits. and the rf exciter. In addition, this linę of transmitters is capable of modulation levels in excess of 125%, with an optional modulation kit allowing higher averagę positive peaks than ever before.

The exciter used in the 820E/F-1 has a highly stable dual ovenless crystal oscillator operating in the 2.1MHz to 4.3-MHz rangę, with division to standard broadcast frequen-cies by integrated Circuit digital dividers. The 10-kW model uses a total of six tubes in the rf driver, power amplifier, and modulator circuits, and requires only two tubę types. The 5-kW model uses one less tubę in the finał rf section.

Collins designed this transmitter for rapid space-saving installation, as well as extended performance. The cabinet measures 69 inches high, 67-7/16 inches wide, by 32 inches deep. Ali power supply components are completely self-contained. For attended operation, all metering and control of the transmitter is accomplished from a control panel which may be located away from the transmitter, and requires no remote control authorization.

Extended Control Panel. The transmitter is suitable for installation at an unattended site, and may be remotely controlled from a distant studio location in the conven-tional manner. As a convenience for attended operation and maintenance the meters and operating Controls are grouped on a 12-1/4- x 19-inch control panel.

RF Exciter. An all solid State unit, the 310W-1 Exciter offers increased frequency stability through operation of the oscillator at two or four times the station frequency. Division to standard broadcast frequencies is obtained through the use of digital integrated circuits. The exciter can be located externally of the transmitter with up to 250 feet of coaxial interconnecting cable.

RF Driver. The rf driver uses two 6146B tubes in parallel, operating Class C. Tuned grid and tuned piąte circuits are employed, with frequency monitor sampling taken from the piąte tank coil.

Output Network. Low pass L-sections transform the 5012 output impedance to 100012 piąte impedance for the 10-kW transmitter, and to 200012 for the 5-kW version. The combined network consists of three series inductances, and three shunt capacitances, plus a second harmonie shunt trap to ground. Overall phase through the networks is -360°, giving a favorable piąte impedance characteristic when operating into loads within the ElA limit for "normal" loads. Motor-driven variable vacuum capacitors in the PA tuning and loading circuits, are controlled from switches on the extendable control panel. PA loading is used to adjust transmitter power output, and can be extended to the remote point through a conventional remote control unit. A phase comparator Circuit is used in the PA stage to automatically control the PA tuning motor as loading changes. Tuning corrections occur at a rapid ratę, well within the time required for loading changes. To assure fail safe operation, the automatic tuning adjustment is disabled until loading changes take place. A manuał/ automatic tuning switch is provided on the control panel to disable the automatic modę when it is desired to perform manuał tuning.

As in every transmitter that Collins produces, the 820E/F-1 series feature superior accessibility and ease of maintenance through the use of vertical parts placement and straightfor-ward design concepts. All cabinet panels may be removed for maintenance and troubleshooting. All voltage test points are brought out to the front panel, and all components are accessible with the removal of the front panels. When space is at a premium, this feature alone will save many hours of valuafole time.

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