COLLINS 821A-2

GENERAL DESCRIPTION

The 821A-2 is a 250-kw AM power amplifier designed for high frequency broadcast and communication service. Any frequency in the 3.95- to 26.5-mc band is tuned within 20 seconds. Direct digital control and monitoring of the amplifier is accomplished by the CCCS (Communication, Computation and Control System) multiplex control system. Through this multiplex control system a station processor (digital computer and associated peripheral devices) transmits control commands such as turn-on, turn-off, frequency change, etc., to the power amplifier and to other equipment in the station complex such as exciters, rf and af switching matrices, test equipment, etc.
Monitor information such as fault indications, current and voltage values is returned to the station processor over the multiplex control system. Thus, the processor can automatically control and monitor the station complex as well as display the operational status of all equipment. The power amplifier is also provided with complete fault, overload, and tune-cycle protection independent of the control/monitor processor.

The 821A-2 consists of four major free-standing sub-units, which are completely factory assembled and tested. The major sub-units (rf, af, power, and cooling) require little disassembly for shipping. This feature results in rapid on-site reassembly and minimizes installation costs. All interconnections between sub-units are overhead. Less than 400 square feet (37 square meters) including access area of indoor floor space is required. An outdoor metal-clad fully enclosed power unit provides component protection, personnel safety protection, and access for servicing the primary power distribution, high-voltage power supply, and oil-filled modulation components.

Solid-state circuitry is used on both the rf and af amplifier chains to the maximum feasible level. Tetrodes provide all remaining power amplification. All power supplies utilize silicon solid-state devices. Filament voltages are regulated within 1 percent for long tube life. Over-all efficiency of the power amplifier is 55 percent.

The need for rf spectrum conservation was a major consideration in the selection of the bandpass output network. Rf cross modulation output below the carrier frequency is reduced by the bandpass network to a degree comparable to spurious radiation reduction above the carrier. Fixed -tuned TVI filters suppress radiation of spurious above the 3.95- to 26.5-mc band.

Thirty-seven plug-in modules are used in the power amplifier. Twenty-six of these modules are interchangeable with at least one other module within the power amplifier. This modular concept results in the rapid replacement of a faulted module as well as a convenient method of spare parts storage. The modules, common to 10 hf and mf power amplifiers, are produced by an automated planar process to insure consistent high quality as well as quick factory response for replacement of spare parts.

Collins 821A-2 diagram

TECHNICAL SPECIFICATIONS
PHYSICAL SPECIFICATIONS
Size (width x depth x height)	RF Unit: 8 x 17 x 7 feet AF Unit: 7 x 3 feet 6 inches x 7 feet HVP Unit: 16 feet 3 inches x 34 feet x 8 feet 7 inches SCU: 16 x 11 x 9 feet
Total Weight	68,500 pounds
Required Floor Space	RF Unit: 136 square feet AF Unit: 24.5 square feet HVP Unit: 553 square feet SCU: 176 square feet Total: 892 square feet
ENVIRONMENTAL SPECIFICATIONS
Ambient Operating Temperature Range	Indoors: +1° to +50°C (+33.8° to +122°F) at sea level; +1° to +30°C (+33.8° to +86°F) at 10,000 feet above msl, linearly derated from sea level to 10,000 feet Outdoors: -35° to +50°C (-31° to +122°F) at sea level; -30° to +30°C (-22° to +86°F) at 10,000 feet above msl, linearly derated from sea level to 10,000 feet
Ambient Nonoperating Temperature Range	Indoors: +1° to +50°C (+33.8° to +122°F) at sea level; +1° to +30°C (+33.8° to +86°F) at 10,000 feet above msl, linearly derated from sea level to 10,000 feet Outdoors: -30° to +50°C (-22° to +122°F) at sea level; -30° to +30°C (-22° to +86°F) at 10,000 feet above msl, linearly derated from sea level to 10,000 feet
Ambient Storage Temperature Range (Equipment dry with no water in the cooling system)	-35° to +60°C (-31° to +140°F)
Ambient Relative Humidity Range	0 to 95°
Altitude	0 to 6,000 feet above msl, with 250-kw output power 6,000 to 10,000 feet above msl, 200-kw output power (Power is reduced by reducing the plate voltage)
ELECTRICAL SPECIFICATIONS
Frequency Range	3.95 to 26.5 MHz in 100 Hz increments
Frequency Stability	Same as exciter
Tuning Time	12 seconds, maximum
RF Input	100 mw to 400 mw, 50 ohms
RF Output	250 kw into 75 ohms, unbalanced, or 300 ohms, balanced, with vswr of 2:1 maximum
Harmonics	At least 80 db below carrier
Carrier Shift	Less than 5% exclusive of power source regulation
Hum and Noise	At least 55 db below 100% modulation
Type of Modulation	High-level AM, FSK, or AM/FSK multiplex
Modulation Capability	Capable of 100% sine wave or clipped sine wave with less than 5% overshoot or droop on the flat top of a 100-hertz sine wave clipped 9 db
Modulation Duty Factor	Continuous at 100% sine wave; 5 minutes on and 15 minutes off at 100% clipped sine wave
Audio Input for 100% Modulation	-2 to +12 dbm, 600/150 ohm, balanced or unbalanced
Audio Response	Within 1 db from the 1000 Hz reference between 100 and 7500 Hz and within 2 db between 50 to 10,000 Hz, at all modulation levels up to 95%
Audio Distortion	Not more than 4% from 100 to 5,000 Hz, not more than 5% from 50 to 7,500 Hz
POWER INPUT SPECIFICATIONS
Primary Power	3-phase, 4160 volts to 13.8 kv, 50 or 60 Hz, 662-kw. No break, -48 volt dc., 7 amp (battery preferred)
Auxiliary Power	Single phase, 120 or 240 volts, 50 or 60 Hz, 15 amp
Power Consumption	Standby: 41-kw Carrier: 452-kw 95% sine-wave modulation: 662-kw

TUBE COMPLEMENT
RF stages		AF stages and modulator		Rectifiers
Number	Type	Number	Type	Number	Type
2	4CV100,000C	2	4CV100,000C
1	4CX3000A	2	4CX350A
2	4CX350A

THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES
	ITU	Country	ITU	Country
	AUS	AUSTRALIA	CAN	CANADA