[Mondial]

A 135V DC supply voltage does not necessarily mean there is a 135 AC signal on the transformer primary. In fact the maximum AC signal is dependent on the volume setting and most likely would much less. You could test the transformer with a much lower voltage, like 10 VAC.

The turns ratio of the primary to secondary will determine the output voltage and it will always be proportional to the input. For example with a 3 to 1 stepdown ratio which might be typical of a Class B driver transformer for a type 19, with 10VAC in you might have 3.3VAC out.

You could easily test the audio output transformer by momentarily touching a 9V battery to the primary (19 tube plate) terminals and listening for a click in the speaker.