EICO 720 TRANSMITTER, 730 MODULATOR, 722 VFO

Eico manufactured a lot of test gear, audio gear, and some ham gear. They even had a surprisingly affordable tri band model 753 sideband rig covering the most popular bands (80, 40, 20) during the early days of SSB, but it drifted a lot. Their best offering is the Eico 720. This rig featured the 6146 final and coverage of 80 through 10 meters. The common deficiency noted with the DX60, Ranger, and others plagued the rotary mode switch in the Eico 720. They just did not handle the AC power switching function well, and often failed. Otherwise I had a lot of fun with mine.

The Eico 730 modulator was a stellar performer. Compare the size of the modulation transformer in the 730 to the one in the Johnson Ranger. It used commonly available 6CA7 hi-fi tubes used in the great Dynakit Stereo 70 amplifier. It used inverse feedback all the way around the modulation transformer, with a special winding for the feedback. It had a great working clipper circuit, which the Ranger and DX60 did not. It also included a novel over modulation indicator which warned when hitting peaks below 0 percent, which would cause splatter. It used a blue eye tube. None of the commercial radios of the time had this feature. The 730 had a multimatch transformer for various impedances, and allowing its use with other transmitters. The stock 720 with a 730 modulator sounds better to me than the Johnson Ranger, and I prefer it to the Ranger for driving a Johnson Desk KW because of the audio quality and the clipper for more punch, if you need it. The desk KW offered an obscure audio driver chassis to allow high level AM when running the Pacemaker as an exciter; Johnson included a clipper circuit similar to the Valiant in the accessory audio unit.

Clipping gets a lot of bad press due to bad design of some rigs, and the over use of clipping by meter-benders. If you use it only to limit the excessive negative peaks, it is imperceptible, except to your neighboring frequencies who do not have to listen to your splatter. You do not need to use any more than that for good conditions. You can always advance it to 3 to 6 dB for a little more punch without objectionable distortion. Much more than that often decreases intelligibility. You can improve both the Ranger and the 730 with minimum changes, but the Ranger will never sound as good as the 730 in my opinion.

The 722 VFO has another tube for good isolation and more drive. It also has an expanded scale on 40, 20, and 15. It has an expanded separate range for the upper end of 10 meters. Of course, it was a lot more expensive than the Heath VF-1.

There is more cost with building a modular system like the 720-730-722. The Ranger was similar in cost, and you had to buy the whole thing at once. A Johnny Novice could run the 720 for 75 watt xtal control, and add the modulator and VFO after upgrading to General. The cheaper DX60 was only screen modulated at about 12 watts output, and the Eico 720 got you around 40 watts output plus the added punch from the clipper. You outgrew the DX60 once you upgraded. The 720 did not make you a big gun on AM, but you had to go to an amp or big iron surplus to get more worthwhile real S units. But at that point in your career, you might be ready for a BC-610 after building the Eico kits up and learning from them.

You can put the 720 on 160 meters with minimum work.

73,
Janis
AB2RA

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