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The AVO Model 8 was the standard for most of the valve era with 20,000 Ω/Volt sensitivity and a black steel case. The meter is powered by a 1.5 Volt cell and a 22.5 Volt battery.
The EM272 has a sensitivity of 315,000 Ω/Volt and the main body is grey plastic. The meter has a current sensitivity down to 3 μA and the amplifier has six transistors. The power is given by both a 15 Volt and a 1.5 V AA cell.
The EA113, introduced in 1971, has a deep blue front panel and a scale length matching the Model 8. Power for the electronics comes from four AA cells.
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