Power Transformer trouble.....?

[vibrovox7reverb]

How can you tell if a power transformer can't handle the current demands? I turn my amp up between 1 and 2 and play for about 30 minutes, and the power transformer is hot to the touch (not so hot I can't touch it, but it does seem problematic that it is getting this warm between 1 and 2). The amp is bedroom volume.

[R.G.]

You're already there. Transformer power handling is determined by how hot it gets (which is easy enough to tell) and by how much temperature rise it can withstand internally, which is difficult-to-impossible to tell unless the manufacturer tells you.

Transformers can be made to operate happily at temperatures hot enough to fry bacon and eggs on. The iron and copper work fine up to the Curie temperature of iron, where the iron loses its magnetic properties, about 1400F/770C. However, the insulation between the copper windings gives up before that. It's the insulation temperature resistance that determines how hot it can get without dying.

So your transformer may be OK. It depends on two things: (1) the temperature rating of the insulation system and (2) whether the amp really draws a lot more current when turned up further. Class A amps do not have a dramatic increase in current draw as they get louder. Class AB biased amps have some increase, Class B has much more change in current drain as power output goes up.

So - you can't tell without more information. I would not worry at all about a transformer that I can still hold my fingertip on at full power. If I can't touch it without damage, I'd worry about the insulation class and also meter the line current change as I turned the power output up.