Note
QST, Jan 1965, p. 119.
QST, May 1966, p. 119.
The models 903A and 913A 2 and 6 meter amps ran 500 watts input with a 4X150A tube. The amplifier required 5 watts drive and included a self contained, solid-state power supply.
Both units operate in Class AB1 for linear modes (SSB, AM, CW, FM, and FSK) and Class C for non-linear modes (FM, PM, and CW). Class AB1 operation offers efficiencies up to 55%, while Class C achieves up to 65% efficiency.
Designed for a power input of 500 watts (PEP, CW, AM peak, or FM). They utilize a grid-driven tetrode configuration requiring a minimum of 5 watts of exciter driving power for full linear output. Attenuation pads (5, 10, or 15 dB) are available for higher-power exciters.
The 903A covers 144 to 148 MHz (2 meters), and the 913A covers 50 to 54 MHz (6 meters). Coverage extends to MARS, CAP, and other military frequency allocations.
Nominal output impedance is 50 ohms, and input impedance is 50 to 75 ohms.
Both models ship standard with a 4X150A tetrode power tube. The sockets also accommodate 4X250B or 7580 tetrodes.
Forced-air cooling is provided via an internal blower motor and ceramic tube chimney system.
Rear Panel Connections: Features RF Input and RF Output connectors, an adjustable Bias Control potentiometer, and two terminal links—Link 1 for switching between Class $\text{AB}_1$ and Class C operation, and Link 2 for connecting external T/R standby relays.
The built-in high-voltage supply uses a solid-state bridge rectifier with 24 controlled avalanche diodes rated at 800 PIV and 750 mA. The bias supply uses a 400 PIV, 500 mA diode. Both units operate on standard 117 VAC, 60 Hz power.
