If the device was built up to original schematic there cannot be such behavior. There is something that prevents the B+ for entering the circuit until the moment of switching off. The original Cornet 2 has a central switch in the mains entrance module ("ac input connector"), so it cannot switch for example heaters only (as far as I understand the tubes glove as usual).
There could be some bad joints somewhere, but it means that you may have sound just by pressing to certain points (you have at least one known point - main switch).