I have a friend who got a custom made neon sign/sculpture and the transformers have gone bad. Unfortunately the two transformer are very old so there is no labeling on what their voltage output was. How can i determine how many volts I need? I don’t want to have too much voltage and damage it. Each transformer controlled 10 of the bulbs, (20 total). The second transformer that is on in the picture partially works but flickers and must also be replaced.