Over the past 4 years I've had new S-30, M-60, and MA-1 amps here and experienced very little, if any, changes from the first time they were fired up to months later.
I suggest your ears were acclimating to the sonics and different presentation of an OTL amplifier.
Dealer disclaimer
I suggest your ears were acclimating to the sonics and different presentation of an OTL amplifier.
Dealer disclaimer