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Tubetown hat IMHO auch nirgends behauptet, dass die Schaltung von Svetlana stammt.

Zitat:How to use a EF86
The Svetlana EF86 is a version of a small pentode which was popular in Europe for use in hi-fi equipment from 1952 through the 1960s.

Unlike the majority of pentodes of this type, the EF86 possesses low distortion, low hum induction and low ionization noise. Further, it has a built-in electrostatic shield, making an external tube shield unnecessary. No other tube in production today has all these features. In addition, the EF86 is an excellent replacement for any EF86/6267 tube previously made.
This bulletin will show a few typical circuit designs which apply the EF86 and make the best use of its unique capabilities.

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Figure 3 shows the EF86 in triode connection. When this is done, the resulting triode is among the lowest-distortion electronic amplifying devices ever made. Typical second-harmonic distortion with 10v RMS output is on the order of 0.05%. This result is achieved without any negative feedback, so this circuit is an excellent choice for high-end audio design. The voltage gain will be about 25 in this connection, making it suitable for line stages.

Quelle: https://www.tube-town.net/diy/sv-ef86/sv-ef86.html

Ich trau der Angabe 0,05% weiterhin nicht.