The Collins 208U10 Power Amplifier

From the Transmitter Web Site



photo Collins 208U-10 PHYSICAL DESCRIPTION

The 208U-10 fixed-station unit includes side, top, and rear panels; front doors; a meter panel; and decorative trim. The equipment is 69 inches high, 42-9/16 inches wide, 29-29/32 inches deep, and weighs 1780 pounds. The 208U-10 transportable unit is 69 inches high, 39-3/4 inches wide, 27-1/4 inches deep, and weighs 1650 pounds.

Power supply unit 1 and rf unit 2 can be removed from the framework for installation in limited space. Access to these two units is from the front; although, rear access is provided if rear space is available. Service and system connections to the 208U-10 are made at the top of the rf unit.

Power supply unit 1 occupies the lower half of the cabinet The power supply unit is 34-7/8 inches high, 36 inches wide, and 23-3/4 inches deep. The power supply unit contains power supply and control circuits which provide all operating voltages for the linear power amplifier. The power supply unit also contains the blower that circulates cooling air through the linear power amplifier compartments. Front access to the power supply unit is provided by a removable panel. The air intake filter assembly is mounted to the front of the removable panel on both the fixed-station 208U-10 and the transportable 208U-10. Local control panel assembly 1A7 contains the necessary controls and indicators required for local operation and testing.

Rf unit 2 occupies the upper half of the cabinet. The rf unit is 26-1/4 inches high, 36 inches wide, and 23-3/4 inches deep. The rf unit is divided into 3 compartments: the PA plate compartment, the PA grid compartment, and the rf control compartment. The PA plate compartment contains the power amplifier tube and plate circuit components, the output network, electronic control amplifier assemblies 2A1 through 2A4, a meter box, and the directional coupler assembly. The power amplifier tube is a 4CX10,000D, which mounts vertically through the casting forming the bottom of the compartment. An air chimney encloses the power amplifier tube and passes through the PA plate compartment to the air exhaust ductwork. The air exhaust ductwork is directly at the top of the cabinet for the fixed-station 208U-10, or directly at the rear of the cabinet for the transportable 208U-10. A smaller chimney directs cooling air across the output network compartments. Mounted on the roof of the PA plate compartment are the terminal boards for external system connections. The bottom of the power amplifier tube extends into the PA grid compartment. The PA grid compartment contains the power amplifier grid and cathode circuit components, including the power amplifier tube filament transformer. The driver amplifier plate circuit components are also located within the PA grid compartment. The plates of the driver amplifier tubes extend into the PA grid compartment The grids and cathodes of the driver amplifier tubes extend into the rf control compartment to the right of the PA grid compartment. The rf control compartment contains the igc (internal gain control) and broadband amplifier stages, the keyer bias supply, and tuning drive assemblies 2A8 through 2A11. The tuning drive assemblies position the driver amplifier plate tuning components in the PA grid compartment and the tunable power amplifier output network components in the PA plate compartment. Amplifier control assembly 2A14 is mounted on the rf control compartment door.


The 208U-10 Linear Power Amplifier is an automatically tuned linear power amplifier which is driven by an external exciter. Not more than 0.2-watt rf input signal is required to drive the linear power amplifier to rated 10.0-kilowatt rf output power. The linear power amplifier is capable of accepting 2-watt average power input during the tune cycle without damage. The equipment will deliver 10-kilowatt rf output power into a 50-ohm load. The rf amplifier stages consist of 2 low-level, wideband rf amplifiers; a plate-tuned driver amplifier; and the power amplifier which operates into a tuned pi-L output network. The linear power amplifier rf circuits are tuned to rf input signals within the 2.0- to 30.0-MHz range during an automatic tune cycle. The automatic tune cycle program provides for coarse positioning the rf tuned circuits, conditional fine tuning of optional external output equipment, and final fine tuning of the rf circuits. The gain of the linear power amplifier is controlled during the tune cycle by internal gain control circuits. The operating point is carefully controlled to provide high efficiency and low intermodulation distortion. A broadband capacitance bridge circuit maintains accurate PA grid neutralization over the entire frequency range. The linear power amplifier develops automatic load control (alc) and transmitter gain control (tgc) voltages which can be applied to the external system exciter to control the system gain.

All operating voltages are provided by power supplies within the power supply unit. The power supplies provide +6250 volts dc for the power amplifier tube plate, -1250 volts dc for the power amplifier tube cathode and for the broadband and driver amplifier tube cathodes, +150-volt dc B+ voltage for the igc amplifier and for signal control bias, 225-volt ac (regulated) tube filament voltage, 115-volt ac servo-motor reference voltage, +28 volts dc for servo amplifier B+ voltage and relay control, and 600-volt dc keying bias.

All power supplies are protected by fuses and a main circuit breaker. Unit and compartment door interlocks are provided for safety, and several overload protective circuits are provided to protect the equipment against malfunction. The equipment can be locally controlled from the cabinet meter and control panel unit 4. System connections can be made at the top of the cabinet for additional remote-controlled operation. Controls are provided on the front panels of the units for local test operation.

Rf output power 10 kilowatts peak envelope power or 10 kilowatts continuous average power
Rf input power 0.2-watt pep. or average for 10-kw output. Capable of accepting up to 2-watt average rf drive during the tune cycle without damage
Frequency range 2 to 30 MHz.
Tuning Automatically tuned to resonance by servo-mechanical means during an automatic tune cycle. Tune cycle manually positioned for local test purposes. Tuning time is not more than 25 seconds with 60-Hz primary power input.
Type of emission SSB, AM, CW, or any other type within the bandwidth and power capabilities.
Rf bandwidth 16 kHz with no more than 0.2-db variation from 3.5 to 30 MHz,
16 kHz, 2.5 to 3.5 db ±1 db,
12 kHz, 2 to 2.5 ±1 db.
Output load impedance 50 ohms: maximum swr of 2 to 1 from 2.0 to 2.5 MHz, maximum swr of 3 to 1 from 2.5 to 30.0 MHz.
Input impedance 50 ohms: maximum swr of 1.5 to 1 from 2.0 to 30.0 MHz.
Intermodulation distortion Third and higher order products not less than 35 db below 1 tone of a 2-tone, signal-producing rated power.
Harmonic output Second harmonic not less than 55 db below fundamental. Higher order harmonics not less than 60 db below fundamental.
Input power requirements One of three 3-phase source configurations.
Volts (ac): 195 to 255, Frequency (Hz): 50 to 60
Volts (ac): 380/440, Frequency (Hz): 50 to 60 (4-wire wye source)
Volts (ac): 195 to 255, Frequency (Hz): 50 to 60/400
Power Consumption
Condition (nominal at 8.0 MHz.)
Filaments on
Plate on
Keyed (static plate currents)
2-tone test at 10 kw pep.
Single tone CW at 10 kw

2.5 kw (nominal), 0.95 power factor.
3.3 kw (nominal), 0.96 power factor.
10.0 kw (nominal), 0.98 power factor.
18.0 kw (nominal), 0.98 power factor.
22.5 kw (nominal), 0.98 power factor.
Temperature -30 °C to +55 °C (-22 °F to +131 °F), continuous duty at rated output.
Altitude Sea level to 10,000 feet, continuous duty at rated output.
Specifications may change without notice

RF stages AF stages and modulator
Number Type Number Type
1 4CX10,000D

3 4CX350A

1 7788