Note
QST, Aug 1958, p. 129.
QST, Apr 1964, p. 139.
Eico short form catalog 1965, p. 41.
Kit or wired.
The Eico 720 is a classic amateur radio transmitter introduced in 1958, primarily targeted at the Novice-class operator but offering an upgrade path. It was sold in both kit form and factory-wired. The transmitter operates CW on the 80, 40, 20, 15, and 10 meter bands, plus the 11-meter band, with a conservative power input of 90 watts (60 watts output) on CW. It also supports 65 watts on AM with the addition of an external plate modulator like the optional Eico 730.
The Eico 720 features a four-tube lineup: a 6CL6 oscillator, a 6AQ5 buffer-multiplier, a 6146 final power amplifier, and a 6AQ5 clamper tube. The clamper tube serves to prevent excessive plate current if the grid drive fails and is part of the keying circuit, which is cathode-keyed but designed with only 12V across the key terminals to prevent shock hazard and sparking. It features one-knob bandswitching and a π-network output capable of matching antennas with impedances from 50 to 1000 ohms. Its low-silhouette design and provisions for an external VFO (like the Eico 722) or crystal control made it a popular and choice for new and upgrading amateurs. The meter has a “Novice limit” marking to help keep input power to the 6146 final to 75 watts for that class of licensee.
Output load impedance: 50–1000Ω
Coverage: 80–10 meters (including 11 meters)
Frequency control: crystal or optional VFO
Connection for an external modulator.
Power: 115 VAC, 60 Hz
Tubes: (1) 6146, (1) 6CL6, (2) 6AQ5, (1) GZ34/5AR4
References
EICO catalog, copyright 1958
Brief description. Radio News, Nov 1958, p. 153.
Review. Electronics World, Jun 1959, p. 82.
Review. CQ, Aug 1959, p. 56.