E F Johnson Variables

[Fred Holnagel]

Does anyone know the marking system for Johnson variables?  I think I may
have it but not sure. I have one each of:
100FD30 and 100ED30. They both are duals so D must mean that. May I
assume the 30 means 3000 Volt rating? Now the difference between the E
and the F?  Different appearance for sure. The stock number on the FD is
155-508. Can't read the other. Thanks es 73's de W7PRV

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