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6e5s (6e5s) Matching the 6E5C

Jacob Roschy Martin Renz Ernst Erb Bernhard Nagel Eilert Menke 
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Forum » Valves / tubes - Semiconductors » VALVES/TUBES / SEMICONDUCTORS in RADIOMUSEUM » 6e5s (6e5s) Matching the 6E5C
Jacob Roschy
Jacob Roschy
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17.May.11 12:05

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Magic eyes like the EM4 or the EM34 requires -16 V control voltage for full output, while the 6E5C requires only -8 V.

If an EM4 or an EM34 is replaced by a 6E5C, even signals of medium strength producing full scale indication, while the range between medium and strong signals no longer can be recognized.

By using a voltage divider, the 6E5C display can be adjusted correctly.

Usually a RC filter is already located in a radio set, which is designed to prevent the fluttering of the display in the rhythm of the modulation. This is shown in Figure 1 A, constituted by R1 and C1.

By adding a further resistor R2 to ground, as shown in Figure 1 - B, a voltage divider is formed, which reduces the control voltage to the 6E5C control grid.

This resistor R2 must be chosen in the manner, that only at strong signals full scale will be achieved.

The value of R2 depends on the available control voltage and on the value of R1. Therefore it must be determined by trial.

You can first install a trimmer of 3 .. 5 meg ohms which has to be adjusted to the desired display. The determined value will then be replaced by a fixed resistor.


If this method is not successful, probably caused by a too low value of R1, one may install a trimming potentiometer R2 of 2 ... 5 meg ohms, as shown in Figure 2 – B, which is to adjust as desired. Following the trimmpot R2 a further capacitor C2 of 10 .. 100 nF is required to suppress ripple effects.

This article was edited 18.May.11 07:30 by Jacob Roschy .