Geophone GF-3F (Turtle)

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Item Geophone GF-3F (Turtle)
Item code
Description Same as 459\8A
Circa 1940
Donor Geophysical Resource Center
Location Houston Geoscience Center
Serial number 3325
Taxonomy GSH459C

The Superior Oil Company “Turtle Geophone” is a variable reluctance moving magnet type that was first developed by Henry Salvatori. An earlier model of the Superior geophone was about 6 inches in diameter and 10 inches high. The variable reluctance geophone had a resonance-like frequency response that was ideal for record character, provided the amplifier had an approximately flat frequency response. This made difficult to design a satisfactory AGC amplifier. Superior’s first AGC amplifier was designed in 1946 by Laurence G. Cowles. The need for a nearly flat frequency response force the designer to use an uncomplicated circuit with a limited control characteristic. That amplifier used only one tube type and 1N34 diodes. The Superior amplifier was redesigned when transistors and FET’s became available with the FET’s used as the variable gain elements. This was believed to be the first use of FET’s in the industry.