Thank you all,
it is understood that then in real operation it will be different from the measurements made only on the transformer, but I will be able to use the measurements for a first comparison between transformers.
I agree and thank Gary Johson, I will put a resistor in series to the primary for matching the impedance, and an 8 ohm resistor on the 8 ohm secondary.
Being a push-pull transformer there should be no problems related to DC current.
Jim Allyn, I only have these transformer data:
Push-pull transformer for EL34 valves.
Secondary impedances: 4 and 8 ohms.
Maximum power: 40W.
-- Cheers
??? Attilio
Attilio