Ralph, do you mean if it has tube regulated voltage, e.g., using
OD3/VR150 type tubes, etc., or something else? How can one visually tell
if a point to point wired preamp has regulated power supply? Thanks.
Whether it is tube regulated or not should not make a difference. An effective regulator will not allow of the sawtooth waveform generated by a rectification to pass to the output. BTW, 0D3s and the like are voltage reference tubes, sort of the vacuum tube equivalent of a zener diode. They are known to make noise and so must be adequately bypassed, and generally are not of much use unless also used with an active regulator circuit, which if in a tube embodiment will have some sort of power tube involved.
It can be hard to tell if the high voltage is regulated but if there are no power devices like a transistor or tube for the task its a pretty good bet that no regulation is employed.