Note
QST, Jul 1965, p. 133.
QST, Mar 1966, p. 127.
QST, Feb 1967, p. 125.
The Swan Mark I is a high-power amateur radio linear amplifier designed around a pair of Eimac 3-400Z triodes operating in a grounded-grid configuration. Capable of delivering up to 2000 watts Peak Envelope Power (PEP) input on SSB and limited to 1000 watts input in CW/TUNE mode, it features an internal dual-changeover relay system that allows the driving transceiver or exciter to feed the antenna directly in "barefoot" mode when the amplifier is switched off or in standby. It covered 80–10 meters.
The unit contains a built-in high-voltage power supply utilizing computer-grade electrolytic capacitors that provide a net capacitance of 40 µF across the plate supply. It comes factory-configured for 230-volt AC operation using a three-wire power cord (two hot lines and a neutral ground) with 20-amp fuses. However, it can be rewired internally for 117-volt AC operation via a four-screw terminal strip near the power transformer, requiring 30-amp line fuses due to high current draw under full load. Because high lethal voltages are present, the power supply requires at least one minute after shutdown for the high-voltage filter capacitors to discharge fully before removing the cabinet or bottom plate.
TUNE-CW Mode: High voltage measures approximately 1600 volts DC in standby and drops to around 1500 volts DC when transmitting with an idling plate current of 0.1 amperes. In this mode, total power input must be kept to 1000 watts—accounting for both the amplifier and the driver stage input—to remain within legal limits. Grid current typically reads between 0.2 and 0.5 amperes depending on driving power.
OPERATE Mode: High voltage increases to roughly 2900 volts DC in standby with zero plate current. When switched to transmit without modulation, the tubes draw 0.18 amperes of idling current while plate voltage settles to 2650 volts DC. Under typical SSB voice modulation averaging 0.35 amperes of plate current (with occasional peaks up to 0.5 amperes), dynamic regulation holds plate voltage around 2500 volts DC.
Interfacing the Mark I requires a short length of 50-ohm coaxial cable (RG-58 or RG-8, preferably under 5 feet) connected from the exciter to the input jack, alongside a two-conductor line attached to the Relay Control jack for transmit keying.
Specifications
– Frequency Range: Covers the 80 through 10 meter bands.
– Power Input: Rated at 2000 watts PEP input for SSB, and 1000 watts input for CW and tune-up.
– Drive Requirements: Requires 100 watts of drive power.
– Relay System: Features a built-in dual changeover relay system for automatic switching between barefoot and linear operation.
– Output Network: Utilizes a wide range pi-output network to match a variety of antenna systems.
Tube Complement
– (2) Eimac 3-400Z
Note: the tubes were not included in the purchase of the amp.
Power Supply: Includes a built-in 117/220 VAC solid-state power supply operating at 2500 volts AC.
