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Take a look at my CORROSION TOPICS page. Lots of unfortunate mistakes and cures. Complete with close-ups!!!


The EICO 710 GDO was one of the more successful tube-type, AC line powered, GDOs. It had a frequency range of 400kHz-250MHz in 8 overlapping ranges. Even though it was a kit, it-as with all other KIT GDOs I am aware of-used pre-wound plug-in coils wound to a 0.5% accuracy on polystyrene forms. Several years ago I was fortunate enough to obtain many 'loose' components from a former EICO engineer's estate. Later, I also obtained an unbuilt EICO 710 kit.

A GDO is basically a wide-range oscillator with a meter in the grid-return line to indicate when the resonant frequency (of the tuned circuit it is loosely coupled to) matches the frequency of the GDO oscillator. That happens because the tuned circuit-under-test absorbs the energy of the oscillator, causing the "dip" of the meter needle downwards. If that oscillator is reasonably calibrated, you then know the approximate resonant frequency of your coil-capacitor combination.

The EICO 710 GDO uses a 1:7 planetary drive on the tuning capacitor. It uses a 6AF4A in a Colpitts oscillator circuit. It is transformer-operated, and uses about 10W of power. The rectifier is a  selenium , and I would strongly recommend: 1) measuring the DC voltage at its output; 2) and then exchanging it for a suitable silicon diode. You should then 3) insert an appropriate dropping resistor to cut the voltage back down to its original value.

Measurements for the EICO 710 GDO are: 2.25" high; 2.6" wide; & 6.9" long. It weighs approximately 3 lbs. The exterior is Steel and Grey wrinkle finish.

The EICO 710-A GDO is a private-labeled solid-state unit identical to the Leader LDM-815 and the Loadstar KDM-6. I had never seen or heard of one 'til I found this one on ebay.



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