Laszlo's Valve Output Stage with Lundahl transformer

[stelios]

.. AC current is transformed down to 88.4 uA RMS. I measured about 64 mV on the secondary. From these two values one can calculate the load represented by the cathode input impedance. It gives 724 ohms. Since I connected 1.5 k parallel with the cathodes, the true cathode input impedance is 1.4 kohm.

err... how can this be : 724 Ohms || 1.5k Ohms = 1.4k Ohms ?
In my books it is: 496 Ohms.

Am I missing sth ?

cheers

Stelios

 

[lcsaszar]

Well, I think I was ambiguous. The input impedance of a SRPP cathode (upper or lower) alone would be 1.4k each, the resulting input impedance including the parallel load resistor is 724 ohms.