Eico 666/667 Tube Tester Current Charts/Graphs

Posted by Ron Reeland (A) on June 29, 2020 at 15:25:35

The Eico 666/667 tube testers instruction manuals include a series of five charts that can be used to determine current flow in the vacuum tube being tested. It is challenging to discern the vertical and horizontal scale graduations values to say the least. And then the value found on the diagonal plot line must be multiplied by a decimal fraction as the plot is for a meter scale reading of "100" only.

I have added current measuring jacks to my Eico so that I can determine current with an external milliamp meter or conventional DVM. Everyone may not wish to make such a modification, but still might be curious to what the current flow is.

After some thought and reviewing the Eico schematic, I was able to deduce just how the chart plots are created and manipulating ohms law provided the numeric data. Additional musing caused me to realize that the data could be duplicated on an Excel worksheet in digital, direct reading, numeric format.

I have included scans of an enlarged Eico chart #1 and my Excel chart that corresponds to it for comparison. Notice that my chart vertical column headed by meter indication of "100" covers the same range as the Eico chart, namely 160 to 40 milliamps top to bottom. All other columns on my chart are a decimal fraction of this column.

For example, each value in column "85" is 85% (.85) times the "100" reference column figure in the same horizontal row. And a meter indication of 115 means it is 115% compared to the referenced column. Thus, Excel does the math for us.

It is easier for you to inspect the chart than it is for me to explain it with words.

I used increments of five for both the meter indication and the plate control setting to fit all data on a single page while using a reasonable text size. A person can just use the nearest increment that corresponds to their Eico meter indication or apply a little interpolation if desired.

Accuracy of current measurement depends on accuracy of shunt resistors R10, R11, R12, R13, R14, as well as basic accuracy of the meter itself. Plate control rheostat R9 is also a factor.

I have generated five charts and there are examples and pertinent information on each one. If you would like a set, E-mail me at ronreeland"AT"msn.com. Change the "AT" to @ of course.

Ron Reeland

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Topic - Eico 666/667 Tube Tester Current Charts/Graphs - Ron Reeland 15:25:35 06/29/20 (0)

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