Microfonic behavior of an Heath ECC81 (12AT7) vs. an new old Telefunken ECC801S.
The Heath tube is horribly sensitive for touching the table, the tube glass, knocking with a fingertip...
I will not use it an this amplifier ;-)
It´s a used tube, maybe it´s defective.
The result is shown in a EL34 PP test circuit.

The unused, new old Telefunken ECC801S is way better!
In the same setup, this tube is just slightly microfinic sensitive.
There are worlds between this two tubes....

Same settings on the oscilloscope.
At the end of the video I set the oscilloscope gain higher, to see the small distortions of the Telefunken ECC801S.

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